Scroll to navigation

SMTPD(8postfix) SMTPD(8postfix)

NAME

smtpd - Postfix SMTP server

SYNOPSIS

smtpd [generic Postfix daemon options]
sendmail -bs

DESCRIPTION


The SMTP server accepts network connection requests and performs zero or more SMTP transactions per connection. Each received message is piped through the cleanup(8) daemon, and is placed into the incoming queue as one single queue file. For this mode of operation, the program expects to be run from the master(8) process manager.

Alternatively, the SMTP server be can run in stand-alone mode; this is traditionally obtained with "sendmail -bs". When the SMTP server runs stand-alone with non $mail_owner privileges, it receives mail even while the mail system is not running, deposits messages directly into the maildrop queue, and disables the SMTP server's access policies. As of Postfix version 2.3, the SMTP server refuses to receive mail from the network when it runs with non $mail_owner privileges.

The SMTP server implements a variety of policies for connection requests, and for parameters given to HELO, ETRN, MAIL FROM, VRFY and RCPT TO commands. They are detailed below and in the main.cf configuration file.

SECURITY



The SMTP server is moderately security-sensitive. It talks to SMTP
    clients and to DNS servers on the network. The SMTP server can be run
    chrooted at fixed low privilege.






STANDARDS


RFC 821 (SMTP protocol)
RFC 1123 (Host requirements)
RFC 1652 (8bit-MIME transport)
RFC 1869 (SMTP service extensions)
RFC 1870 (Message size declaration)
RFC 1985 (ETRN command)
RFC 2034 (SMTP enhanced status codes)
RFC 2554 (AUTH command)
RFC 2821 (SMTP protocol)
RFC 2920 (SMTP pipelining)
RFC 3030 (CHUNKING without BINARYMIME)
RFC 3207 (STARTTLS command)
RFC 3461 (SMTP DSN extension)
RFC 3463 (Enhanced status codes)
RFC 3848 (ESMTP transmission types)
RFC 4409 (Message submission)
RFC 4954 (AUTH command)
RFC 5321 (SMTP protocol)
RFC 6531 (Internationalized SMTP)
RFC 6533 (Internationalized Delivery Status Notifications)
RFC 7505 ("Null MX" No Service Resource Record)






DIAGNOSTICS




Problems and transactions are logged to syslogd(8) or
    postlogd(8).


Depending on the setting of the notify_classes parameter,
    the postmaster is notified of bounces, protocol problems, policy violations,
    and of other trouble.






CONFIGURATION PARAMETERS




Changes to main.cf are picked up automatically, as
    smtpd(8) processes run for only a limited amount of time. Use the
    command "postfix reload" to speed up a change.


The text below provides only a parameter summary. See
    postconf(5) for more details including examples.






COMPATIBILITY CONTROLS




The following parameters work around implementation errors in
    other software, and/or allow you to override standards in order to prevent
    undesirable use.
  





  

  
Enable interoperability with remote SMTP clients that implement an
      obsolete version of the AUTH command (RFC 4954).

  

  
Disable the SMTP VRFY command.

  

  
List of commands that the Postfix SMTP server replies to with "250
      Ok", without doing any syntax checks and without changing state.

  

  
Require that addresses received in SMTP MAIL FROM and RCPT TO commands are
      enclosed with <>, and that those addresses do not contain RFC 822
      style comments or phrases.




Available in Postfix version 2.1 and later:



  

  
Request that the Postfix SMTP server rejects mail from unknown sender
      addresses, even when no explicit reject_unlisted_sender access restriction
      is specified.

  

  
What remote SMTP clients the Postfix SMTP server will not offer AUTH
      support to.




Available in Postfix version 2.2 and later:



  

  
Lookup tables, indexed by the remote SMTP client address, with case
      insensitive lists of EHLO keywords (pipelining, starttls, auth, etc.) that
      the Postfix SMTP server will not send in the EHLO response to a remote
      SMTP client.

  

  
A case insensitive list of EHLO keywords (pipelining, starttls, auth,
      etc.) that the Postfix SMTP server will not send in the EHLO response to a
      remote SMTP client.

  

  
Postpone the start of an SMTP mail transaction until a valid RCPT TO
      command is received.




Available in Postfix version 2.3 and later:



  

  
Force the Postfix SMTP server to issue a TLS session id, even when TLS
      session caching is turned off (smtpd_tls_session_cache_database is
    empty).




Available in Postfix version 2.6 and later:



  

  
An optional workaround for routers that break TCP window scaling.




Available in Postfix version 2.7 and later:



  

  
A mechanism to transform commands from remote SMTP clients.




Available in Postfix version 2.9 - 3.6:



  

  
Change the behavior of the smtpd_timeout and smtpd_starttls_timeout time
      limits, from a time limit per read or write system call, to a time limit
      to send or receive a complete record (an SMTP command line, SMTP response
      line, SMTP message content line, or TLS protocol message).




Available in Postfix version 3.0 and later:



  

  
Optional filter for Postfix SMTP server DNS lookup results.




Available in Postfix 3.5 and later:



  

  
The email address form that will be used in non-debug logging (info,
      warning, etc.).




Available in Postfix version 3.6 and later:



  

  
Evaluate smtpd_relay_restrictions before
    smtpd_recipient_restrictions.

  

  
Optional setting that avoids lookups in the services(5)
    database.




Available in Postfix version 3.7 and later:



  

  
Change the behavior of the smtpd_timeout and smtpd_starttls_timeout time
      limits, from a time limit per plaintext or TLS read or write call, to a
      combined time limit for receiving a complete SMTP request and for sending
      a complete SMTP response.

  

  
The minimum plaintext data transfer rate in bytes/second for DATA and BDAT
      requests, when deadlines are enabled with smtpd_per_request_deadline.








ADDRESS REWRITING CONTROLS




See the ADDRESS_REWRITING_README document for a detailed
    discussion of Postfix address rewriting.



  

  
Enable or disable recipient validation, built-in content filtering, or
      address mapping.




Available in Postfix version 2.2 and later:



  

  
Rewrite or add message headers in mail from these clients, updating
      incomplete addresses with the domain name in $myorigin or $mydomain, and
      adding missing headers.








BEFORE-SMTPD PROXY AGENT




Available in Postfix version 2.10 and later:



  

  
The name of the proxy protocol used by an optional before-smtpd proxy
      agent.

  

  
The time limit for the proxy protocol specified with the
      smtpd_upstream_proxy_protocol parameter.








AFTER QUEUE EXTERNAL CONTENT INSPECTION CONTROLS




As of version 1.0, Postfix can be configured to send new mail to
    an external content filter AFTER the mail is queued. This content filter is
    expected to inject mail back into a (Postfix or other) MTA for further
    delivery. See the FILTER_README document for details.



  

  
After the message is queued, send the entire message to the specified
      transport:destination.








BEFORE QUEUE EXTERNAL CONTENT INSPECTION CONTROLS




As of version 2.1, the Postfix SMTP server can be configured to
    send incoming mail to a real-time SMTP-based content filter BEFORE mail is
    queued. This content filter is expected to inject mail back into Postfix.
    See the SMTPD_PROXY_README document for details on how to configure and
    operate this feature.



  

  
The hostname and TCP port of the mail filtering proxy server.

  

  
How the Postfix SMTP server announces itself to the proxy filter.

  

  
List of options that control how the Postfix SMTP server communicates with
      a before-queue content filter.

  

  
The time limit for connecting to a proxy filter and for sending or
      receiving information.








BEFORE QUEUE MILTER CONTROLS




As of version 2.3, Postfix supports the Sendmail version 8 Milter
    (mail filter) protocol. These content filters run outside Postfix. They can
    inspect the SMTP command stream and the message content, and can request
    modifications before mail is queued. For details see the MILTER_README
    document.



  

  
A list of Milter (mail filter) applications for new mail that arrives via
      the Postfix smtpd(8) server.

  

  
The mail filter protocol version and optional protocol extensions for
      communication with a Milter application; prior to Postfix 2.6 the default
      protocol is 2.

  

  
The default action when a Milter (mail filter) response is unavailable
      (for example, bad Postfix configuration or Milter failure).

  

  
The {daemon_name} macro value for Milter (mail filter) applications.

  

  
The {v} macro value for Milter (mail filter) applications.

  

  
The time limit for connecting to a Milter (mail filter) application, and
      for negotiating protocol options.

  

  
The time limit for sending an SMTP command to a Milter (mail filter)
      application, and for receiving the response.

  

  
The time limit for sending message content to a Milter (mail filter)
      application, and for receiving the response.

  

  
The macros that are sent to Milter (mail filter) applications after
      completion of an SMTP connection.

  

  
The macros that are sent to Milter (mail filter) applications after the
      SMTP HELO or EHLO command.

  

  
The macros that are sent to Milter (mail filter) applications after the
      SMTP MAIL FROM command.

  

  
The macros that are sent to Milter (mail filter) applications after the
      SMTP RCPT TO command.

  

  
The macros that are sent to version 4 or higher Milter (mail filter)
      applications after the SMTP DATA command.

  

  
The macros that are sent to version 3 or higher Milter (mail filter)
      applications after an unknown SMTP command.

  

  
The macros that are sent to Milter (mail filter) applications after the
      end of the message header.

  

  
The macros that are sent to Milter (mail filter) applications after the
      message end-of-data.




Available in Postfix version 3.1 and later:



  

  
Optional list of name=value pairs that specify default values for
      arbitrary macros that Postfix may send to Milter applications.




Available in Postfix version 3.2 and later:



  

  
Lookup tables with Milter settings per remote SMTP client IP address.








GENERAL CONTENT INSPECTION CONTROLS




The following parameters are applicable for both built-in and
    external content filters.


Available in Postfix version 2.1 and later:



  

  
Enable or disable recipient validation, built-in content filtering, or
      address mapping.








EXTERNAL CONTENT INSPECTION CONTROLS




The following parameters are applicable for both before-queue and
    after-queue content filtering.


Available in Postfix version 2.1 and later:



  

  
What remote SMTP clients are allowed to use the XFORWARD feature.








SASL AUTHENTICATION CONTROLS




Postfix SASL support (RFC 4954) can be used to authenticate remote
    SMTP clients to the Postfix SMTP server, and to authenticate the Postfix
    SMTP client to a remote SMTP server. See the SASL_README document for
    details.



  

  
Enable interoperability with remote SMTP clients that implement an
      obsolete version of the AUTH command (RFC 4954).

  

  
Enable SASL authentication in the Postfix SMTP server.

  

  
The name of the Postfix SMTP server's local SASL authentication
    realm.

  

  
Postfix SMTP server SASL security options; as of Postfix 2.3 the list of
      available features depends on the SASL server implementation that is
      selected with smtpd_sasl_type.

  

  
Optional lookup table with the SASL login names that own the sender (MAIL
      FROM) addresses.




Available in Postfix version 2.1 and later:



  

  
What remote SMTP clients the Postfix SMTP server will not offer AUTH
      support to.




Available in Postfix version 2.1 and 2.2:



  

  
The application name that the Postfix SMTP server uses for SASL server
      initialization.




Available in Postfix version 2.3 and later:



  

  
Report the SASL authenticated user name in the smtpd(8) Received
      message header.

  

  
Implementation-specific information that the Postfix SMTP server passes
      through to the SASL plug-in implementation that is selected with
      smtpd_sasl_type.

  

  
The SASL plug-in type that the Postfix SMTP server should use for
      authentication.




Available in Postfix version 2.5 and later:



  

  
Search path for Cyrus SASL application configuration files, currently used
      only to locate the $smtpd_sasl_path.conf file.




Available in Postfix version 2.11 and later:



  

  
The service name that is passed to the SASL plug-in that is selected with
      smtpd_sasl_type and smtpd_sasl_path.




Available in Postfix version 3.4 and later:



  

  
The maximum length of a SASL client's response to a server challenge.




Available in Postfix 3.6 and later:



  

  
If non-empty, a filter for the SASL mechanism names that the Postfix SMTP
      server will announce in the EHLO response.








STARTTLS SUPPORT CONTROLS




Detailed information about STARTTLS configuration may be found in
    the TLS_README document.



  

  
The SMTP TLS security level for the Postfix SMTP server; when a non-empty
      value is specified, this overrides the obsolete parameters smtpd_use_tls
      and smtpd_enforce_tls.

  

  
The SASL authentication security options that the Postfix SMTP server uses
      for TLS encrypted SMTP sessions.

  

  
The time limit for Postfix SMTP server write and read operations during
      TLS startup and shutdown handshake procedures.

  

  
A file containing (PEM format) CA certificates of root CAs trusted to sign
      either remote SMTP client certificates or intermediate CA
    certificates.

  

  
A directory containing (PEM format) CA certificates of root CAs trusted to
      sign either remote SMTP client certificates or intermediate CA
      certificates.

  

  
Force the Postfix SMTP server to issue a TLS session id, even when TLS
      session caching is turned off (smtpd_tls_session_cache_database is
    empty).

  

  
Ask a remote SMTP client for a client certificate.

  

  
When TLS encryption is optional in the Postfix SMTP server, do not
      announce or accept SASL authentication over unencrypted connections.

  

  
The verification depth for remote SMTP client certificates.

  

  
File with the Postfix SMTP server RSA certificate in PEM format.

  

  
List of ciphers or cipher types to exclude from the SMTP server cipher
      list at all TLS security levels.

  

  
File with the Postfix SMTP server DSA certificate in PEM format.

  

  
File with DH parameters that the Postfix SMTP server should use with
      non-export EDH ciphers.

  

  
File with DH parameters that the Postfix SMTP server should use with
      export-grade EDH ciphers.

  

  
File with the Postfix SMTP server DSA private key in PEM format.

  

  
File with the Postfix SMTP server RSA private key in PEM format.

  

  
Enable additional Postfix SMTP server logging of TLS activity.

  

  
The minimum TLS cipher grade that the Postfix SMTP server will use with
      mandatory TLS encryption.

  

  
Additional list of ciphers or cipher types to exclude from the Postfix
      SMTP server cipher list at mandatory TLS security levels.

  

  
TLS protocols accepted by the Postfix SMTP server with mandatory TLS
      encryption.

  

  
Request that the Postfix SMTP server produces Received: message headers
      that include information about the protocol and cipher used, as well as
      the remote SMTP client CommonName and client certificate issuer
      CommonName.

  

  
With mandatory TLS encryption, require a trusted remote SMTP client
      certificate in order to allow TLS connections to proceed.

  

  
Run the Postfix SMTP server in TLS "wrapper" mode, instead of
      using the STARTTLS command.

  

  
The number of pseudo-random bytes that an smtp(8) or
      smtpd(8) process requests from the tlsmgr(8) server in order
      to seed its internal pseudo random number generator (PRNG).

  

  
The OpenSSL cipherlist for "high" grade ciphers.

  

  
The OpenSSL cipherlist for "medium" or higher grade
    ciphers.

  

  
The OpenSSL cipherlist for "NULL" grade ciphers that provide
      authentication without encryption.




Available in Postfix version 2.3..3.7:



  

  
The OpenSSL cipherlist for "low" or higher grade ciphers.

  

  
The OpenSSL cipherlist for "export" or higher grade
    ciphers.




Available in Postfix version 2.5 and later:



  

  
The message digest algorithm to construct remote SMTP client-certificate
      fingerprints or public key fingerprints (Postfix 2.9 and later) for
      check_ccert_access and permit_tls_clientcerts.




Available in Postfix version 2.6 and later:



  

  
TLS protocols accepted by the Postfix SMTP server with opportunistic TLS
      encryption.

  

  
The minimum TLS cipher grade that the Postfix SMTP server will use with
      opportunistic TLS encryption.

  

  
File with the Postfix SMTP server ECDSA certificate in PEM format.

  

  
File with the Postfix SMTP server ECDSA private key in PEM format.

  

  
The Postfix SMTP server security grade for ephemeral elliptic-curve
      Diffie-Hellman (EECDH) key exchange.

  

  
The elliptic curve used by the Postfix SMTP server for sensibly strong
      ephemeral ECDH key exchange.

  

  
The elliptic curve used by the Postfix SMTP server for maximally strong
      ephemeral ECDH key exchange.




Available in Postfix version 2.8 and later:



  

  
With SSLv3 and later, use the Postfix SMTP server's cipher preference
      order instead of the remote client's cipher preference order.

  

  
List or bit-mask of OpenSSL bug work-arounds to disable.




Available in Postfix version 2.11 and later:



  

  
The name of the tlsmgr(8) service entry in master.cf.




Available in Postfix version 3.0 and later:



  

  
Algorithm used to encrypt RFC5077 TLS session tickets.




Available in Postfix version 3.2 and later:



  

  
The prioritized list of elliptic curves supported by the Postfix SMTP
      client and server.




Available in Postfix version 3.4 and later:



  

  
List of one or more PEM files, each holding one or more private keys
      directly followed by a corresponding certificate chain.

  

  
Optional lookup tables that map names received from remote SMTP clients
      via the TLS Server Name Indication (SNI) extension to the appropriate keys
      and certificate chains.




Available in Postfix 3.5, 3.4.6, 3.3.5, 3.2.10, 3.1.13 and
  later:



  

  
A workaround for implementations that hang Postfix while shutting down a
      TLS session, until Postfix times out.




Available in Postfix version 3.8 and later:



  

  
The prioritized list of finite-field Diffie-Hellman ephemeral (FFDHE) key
      exchange groups supported by the Postfix SMTP client and server.




Available in Postfix 3.9, 3.8.1, 3.7.6, 3.6.10, 3.5.20 and
  later:



  

  
Optional configuration file with baseline OpenSSL settings.

  

  
The application name passed by Postfix to OpenSSL library initialization
      functions.




Available in Postfix version 3.9 and later:



  

  
Request that remote SMTP clients send an RFC7250 raw public key instead of
      an X.509 certificate, when asking for or requiring client
    authentication.








OBSOLETE STARTTLS CONTROLS




The following configuration parameters exist for compatibility
    with Postfix versions before 2.3. Support for these will be removed in a
    future release.



  

  
Opportunistic TLS: announce STARTTLS support to remote SMTP clients, but
      do not require that clients use TLS encryption.

  

  
Mandatory TLS: announce STARTTLS support to remote SMTP clients, and
      require that clients use TLS encryption.

  

  
Obsolete Postfix < 2.3 control for the Postfix SMTP server TLS cipher
      list.








SMTPUTF8 CONTROLS




Preliminary SMTPUTF8 support is introduced with Postfix 3.0.



  

  
Enable preliminary SMTPUTF8 support for the protocols described in RFC
      6531, RFC 6532, and RFC 6533.

  

  
Enable stricter enforcement of the SMTPUTF8 protocol.

  

  
Detect that a message requires SMTPUTF8 support for the specified mail
      origin classes.




Available in Postfix version 3.2 and later:



  

  
Enable 'transitional' compatibility between IDNA2003 and IDNA2008, when
      converting UTF-8 domain names to/from the ASCII form that is used for DNS
      lookups.








VERP SUPPORT CONTROLS




With VERP style delivery, each recipient of a message receives a
    customized copy of the message with his/her own recipient address encoded in
    the envelope sender address. The VERP_README file describes configuration
    and operation details of Postfix support for variable envelope return path
    addresses. VERP style delivery is requested with the SMTP XVERP command or
    with the "sendmail -V" command-line option and is available in
    Postfix version 1.1 and later.



  

  
The two default VERP delimiter characters.

  

  
The characters Postfix accepts as VERP delimiter characters on the Postfix
      sendmail(1) command line and in SMTP commands.




Available in Postfix version 1.1 and 2.0:



  

  
What remote SMTP clients are allowed to specify the XVERP command.




Available in Postfix version 2.1 and later:



  

  
What remote SMTP clients are allowed to specify the XVERP command.








TROUBLE SHOOTING CONTROLS




The DEBUG_README document describes how to debug parts of the
    Postfix mail system. The methods vary from making the software log a lot of
    detail, to running some daemon processes under control of a call tracer or
    debugger.



  

  
The increment in verbose logging level when a nexthop destination, remote
      client or server name or network address matches a pattern given with the
      debug_peer_list parameter.

  

  
Optional list of nexthop destination, remote client or server name or
      network address patterns that, if matched, cause the verbose logging level
      to increase by the amount specified in $debug_peer_level.

  

  
The recipient of postmaster notifications about mail delivery problems
      that are caused by policy, resource, software or protocol errors.

  

  
What categories of Postfix-generated mail are subject to before-queue
      content inspection by non_smtpd_milters, header_checks and
    body_checks.

  

  
The list of error classes that are reported to the postmaster.

  
  
Optional information that is appended after each Postfix SMTP server 4XX
      or 5XX response.

  

  
Safety net to keep mail queued that would otherwise be returned to the
      sender.




Available in Postfix version 2.1 and later:



  

  
What remote SMTP clients are allowed to use the XCLIENT feature.




Available in Postfix version 2.10 and later:



  

  
Enable logging of the named "permit" actions in SMTP server
      access lists (by default, the SMTP server logs "reject" actions
      but not "permit" actions).








KNOWN VERSUS UNKNOWN RECIPIENT CONTROLS




As of Postfix version 2.0, the SMTP server rejects mail for
    unknown recipients. This prevents the mail queue from clogging up with
    undeliverable MAILER-DAEMON messages. Additional information on this topic
    is in the LOCAL_RECIPIENT_README and ADDRESS_CLASS_README documents.



  

  
Display the name of the recipient table in the "User unknown"
      responses.

  

  
Optional address mapping lookup tables for message headers and
    envelopes.

  

  
Optional address mapping lookup tables for envelope and header recipient
      addresses.

  

  
Optional address mapping lookup tables for envelope and header sender
      addresses.




Parameters concerning known/unknown local recipients:



  

  
The list of domains that are delivered via the $local_transport mail
      delivery transport.

  

  
The local network interface addresses that this mail system receives mail
      on.

  

  
The remote network interface addresses that this mail system receives mail
      on by way of a proxy or network address translation unit.

  

  
The Internet protocols Postfix will attempt to use when making or
      accepting connections.

  

  
Lookup tables with all names or addresses of local recipients: a recipient
      address is local when its domain matches $mydestination, $inet_interfaces
      or $proxy_interfaces.

  

  
The numerical Postfix SMTP server response code when a recipient address
      is local, and $local_recipient_maps specifies a list of lookup tables that
      does not match the recipient.




Parameters concerning known/unknown recipients of relay
    destinations:



  

  
What destination domains (and subdomains thereof) this system will relay
      mail to.

  

  
Optional lookup tables with all valid addresses in the domains that match
      $relay_domains.

  

  
The numerical Postfix SMTP server reply code when a recipient address
      matches $relay_domains, and relay_recipient_maps specifies a list of
      lookup tables that does not match the recipient address.




Parameters concerning known/unknown recipients in virtual alias
    domains:



  

  
Postfix is the final destination for the specified list of virtual alias
      domains, that is, domains for which all addresses are aliased to addresses
      in other local or remote domains.

  

  
Optional lookup tables with aliases that apply to all recipients:
      local(8), virtual, and remote; this is unlike alias_maps that apply
      only to local(8) recipients.

  

  
The Postfix SMTP server reply code when a recipient address matches
      $virtual_alias_domains, and $virtual_alias_maps specifies a list of lookup
      tables that does not match the recipient address.




Parameters concerning known/unknown recipients in virtual mailbox
    domains:



  

  
Postfix is the final destination for the specified list of domains; mail
      is delivered via the $virtual_transport mail delivery transport.

  

  
Optional lookup tables with all valid addresses in the domains that match
      $virtual_mailbox_domains.

  

  
The Postfix SMTP server reply code when a recipient address matches
      $virtual_mailbox_domains, and $virtual_mailbox_maps specifies a list of
      lookup tables that does not match the recipient address.








RESOURCE AND RATE CONTROLS




The following parameters limit resource usage by the SMTP server
    and/or control client request rates.



  

  
Upon input, long lines are chopped up into pieces of at most this length;
      upon delivery, long lines are reconstructed.

  

  
The minimal amount of free space in bytes in the queue file system that is
      needed to receive mail.

  

  
The maximal size in bytes of a message, including envelope
    information.

  

  
The maximal number of recipients that the Postfix SMTP server accepts per
      message delivery request.

  

  
When the Postfix SMTP server wants to send an SMTP server response, how
      long the Postfix SMTP server will wait for an underlying network write
      operation to complete; and when the Postfix SMTP server Postfix wants to
      receive an SMTP client request, how long the Postfix SMTP server will wait
      for an underlying network read operation to complete.

  

  
The maximal number of lines in the Postfix SMTP server command history
      before it is flushed upon receipt of EHLO, RSET, or end of DATA.




Available in Postfix version 2.3 and later:



  

  
Attempt to look up the remote SMTP client hostname, and verify that the
      name matches the client IP address.




The per SMTP client connection count and request rate limits are
    implemented in co-operation with the anvil(8) service, and are
    available in Postfix version 2.2 and later.



  

  
How many simultaneous connections any client is allowed to make to this
      service.

  

  
The maximal number of connection attempts any client is allowed to make to
      this service per time unit.

  

  
The maximal number of message delivery requests that any client is allowed
      to make to this service per time unit, regardless of whether or not
      Postfix actually accepts those messages.

  

  
The maximal number of recipient addresses that any client is allowed to
      send to this service per time unit, regardless of whether or not Postfix
      actually accepts those recipients.

  

  
Clients that are excluded from smtpd_client_*_count/rate_limit
      restrictions.




Available in Postfix version 2.3 and later:



  

  
The maximal number of new (i.e., uncached) TLS sessions that a remote SMTP
      client is allowed to negotiate with this service per time unit.




Available in Postfix version 2.9 - 3.6:



  

  
Change the behavior of the smtpd_timeout and smtpd_starttls_timeout time
      limits, from a time limit per read or write system call, to a time limit
      to send or receive a complete record (an SMTP command line, SMTP response
      line, SMTP message content line, or TLS protocol message).




Available in Postfix version 3.1 and later:



  

  
The maximal number of AUTH commands that any client is allowed to send to
      this service per time unit, regardless of whether or not Postfix actually
      accepts those commands.




Available in Postfix version 3.7 and later:



  

  
Change the behavior of the smtpd_timeout and smtpd_starttls_timeout time
      limits, from a time limit per plaintext or TLS read or write call, to a
      combined time limit for receiving a complete SMTP request and for sending
      a complete SMTP response.

  

  
The minimum plaintext data transfer rate in bytes/second for DATA and BDAT
      requests, when deadlines are enabled with smtpd_per_request_deadline.

  

  
The format of the Postfix-generated From: header.




Available in Postfix version 3.8 and later:



  

  
Aggregate smtpd_client_*_count and smtpd_client_*_rate statistics by IPv4
      network blocks with the specified network prefix.

  

  
Aggregate smtpd_client_*_count and smtpd_client_*_rate statistics by IPv6
      network blocks with the specified network prefix.




Available in Postfix 3.9, 3.8.1, 3.7.6, 3.6.10, 3.5.20 and
  later:



  

  
Disconnect remote SMTP clients that violate RFC 2920 (or 5321) command
      pipelining constraints.




Available in Postfix 3.9, 3.8.4, 3.7.9, 3.6.13, 3.5.23 and
  later:



  

  
Reject or restrict input lines from an SMTP client that end in <LF>
      instead of the standard <CR><LF>.

  

  
Exclude the specified clients from smtpd_forbid_bare_newline
    enforcement.




Available in Postfix 3.9, 3.8.5, 3.7.10, 3.6.14, 3.5.24 and
  later:



  

  
The numerical Postfix SMTP server response code when rejecting a request
      with "smtpd_forbid_bare_newline = reject".








TARPIT CONTROLS




When a remote SMTP client makes errors, the Postfix SMTP server
    can insert delays before responding. This can help to slow down run-away
    software. The behavior is controlled by an error counter that counts the
    number of errors within an SMTP session that a client makes without
    delivering mail.



  

  
With Postfix version 2.1 and later: the SMTP server response delay after a
      client has made more than $smtpd_soft_error_limit errors, and fewer than
      $smtpd_hard_error_limit errors, without delivering mail.

  

  
The number of errors a remote SMTP client is allowed to make without
      delivering mail before the Postfix SMTP server slows down all its
      responses.

  

  
The maximal number of errors a remote SMTP client is allowed to make
      without delivering mail.

  

  
The number of junk commands (NOOP, VRFY, ETRN or RSET) that a remote SMTP
      client can send before the Postfix SMTP server starts to increment the
      error counter with each junk command.




Available in Postfix version 2.1 and later:



  

  
The number of recipients that a remote SMTP client can send in excess of
      the limit specified with $smtpd_recipient_limit, before the Postfix SMTP
      server increments the per-session error count for each excess
    recipient.








ACCESS POLICY DELEGATION CONTROLS




As of version 2.1, Postfix can be configured to delegate access
    policy decisions to an external server that runs outside Postfix. See the
    file SMTPD_POLICY_README for more information.



  

  
The time after which an idle SMTPD policy service connection is
    closed.

  

  
The time after which an active SMTPD policy service connection is
    closed.

  

  
The time limit for connecting to, writing to, or receiving from a
      delegated SMTPD policy server.




Available in Postfix version 3.0 and later:



  

  
The default action when an SMTPD policy service request fails.

  

  
The maximal number of requests per SMTPD policy service connection, or
      zero (no limit).

  

  
The maximal number of attempts to send an SMTPD policy service request
      before giving up.

  

  
The delay between attempts to resend a failed SMTPD policy service
      request.




Available in Postfix version 3.1 and later:



  

  
Optional information that the Postfix SMTP server specifies in the
      "policy_context" attribute of a policy service request
      (originally, to share the same service endpoint among multiple
      check_policy_service clients).








ACCESS CONTROLS




The SMTPD_ACCESS_README document gives an introduction to all the
    SMTP server access control features.



  

  
Wait until the RCPT TO command before evaluating
      $smtpd_client_restrictions, $smtpd_helo_restrictions and
      $smtpd_sender_restrictions, or wait until the ETRN command before
      evaluating $smtpd_client_restrictions and $smtpd_helo_restrictions.

  

  
A list of Postfix features where the pattern "example.com" also
      matches subdomains of example.com, instead of requiring an explicit
      ".example.com" pattern.

  

  
Optional restrictions that the Postfix SMTP server applies in the context
      of a client connection request.

  

  
Require that a remote SMTP client introduces itself with the HELO or EHLO
      command before sending the MAIL command or other commands that require
      EHLO negotiation.

  

  
Optional restrictions that the Postfix SMTP server applies in the context
      of a client HELO command.

  

  
Optional restrictions that the Postfix SMTP server applies in the context
      of a client MAIL FROM command.

  

  
Optional restrictions that the Postfix SMTP server applies in the context
      of a client RCPT TO command, after smtpd_relay_restrictions.

  

  
Optional restrictions that the Postfix SMTP server applies in the context
      of a client ETRN command.

  

  
Forward mail with sender-specified routing (user[@%!]remote[@%!]site) from
      untrusted clients to destinations matching $relay_domains.

  

  
User-defined aliases for groups of access restrictions.

  

  
The lookup key to be used in SMTP access(5) tables instead of the
      null sender address.

  

  
Restrict the use of the permit_mx_backup SMTP access feature to only
      domains whose primary MX hosts match the listed networks.




Available in Postfix version 2.0 and later:



  

  
Optional access restrictions that the Postfix SMTP server applies in the
      context of the SMTP DATA command.

  

  
What characters are allowed in $name expansions of RBL reply
    templates.




Available in Postfix version 2.1 and later:



  

  
Request that the Postfix SMTP server rejects mail from unknown sender
      addresses, even when no explicit reject_unlisted_sender access restriction
      is specified.

  

  
Request that the Postfix SMTP server rejects mail for unknown recipient
      addresses, even when no explicit reject_unlisted_recipient access
      restriction is specified.




Available in Postfix version 2.2 and later:



  

  
Optional access restrictions that the Postfix SMTP server applies in the
      context of the SMTP END-OF-DATA command.




Available in Postfix version 2.10 and later:



  

  
Access restrictions for mail relay control that the Postfix SMTP server
      applies in the context of the RCPT TO command, before
      smtpd_recipient_restrictions.








SENDER AND RECIPIENT ADDRESS VERIFICATION CONTROLS




Postfix version 2.1 introduces sender and recipient address
    verification. This feature is implemented by sending probe email messages
    that are not actually delivered. This feature is requested via the
    reject_unverified_sender and reject_unverified_recipient access
    restrictions. The status of verification probes is maintained by the
    verify(8) server. See the file ADDRESS_VERIFICATION_README for
    information about how to configure and operate the Postfix sender/recipient
    address verification service.



  

  
How many times to query the verify(8) service for the completion of
      an address verification request in progress.

  

  
The delay between queries for the completion of an address verification
      request in progress.

  

  
The sender address to use in address verification probes; prior to Postfix
      2.5 the default was "postmaster".

  

  
The numerical Postfix SMTP server response code when a recipient address
      is rejected by the reject_unverified_sender restriction.

  

  
The numerical Postfix SMTP server response when a recipient address is
      rejected by the reject_unverified_recipient restriction.




Available in Postfix version 2.6 and later:



  

  
The numerical Postfix SMTP server response code when a sender address
      probe fails due to a temporary error condition.

  

  
The numerical Postfix SMTP server response when a recipient address probe
      fails due to a temporary error condition.

  

  
The Postfix SMTP server's reply when rejecting mail with
      reject_unverified_sender.

  

  
The Postfix SMTP server's reply when rejecting mail with
      reject_unverified_recipient.

  

  
The Postfix SMTP server's action when reject_unverified_sender fails due
      to a temporary error condition.

  

  
The Postfix SMTP server's action when reject_unverified_recipient fails
      due to a temporary error condition.




Available with Postfix 2.9 and later:



  

  
The time between changes in the time-dependent portion of address
      verification probe sender addresses.








ACCESS CONTROL RESPONSES




The following parameters control numerical SMTP reply codes and/or
    text responses.



  

  
The numerical Postfix SMTP server response code for an access(5)
      map "reject" action.

  

  
The numerical Postfix SMTP server response code when a remote SMTP client
      request is rejected by the "defer" restriction.

  

  
The numerical Postfix SMTP server response code when the client HELO or
      EHLO command parameter is rejected by the reject_invalid_helo_hostname
      restriction.

  

  
The numerical Postfix SMTP server response code when a remote SMTP client
      request is blocked by the reject_rbl_client, reject_rhsbl_client,
      reject_rhsbl_reverse_client, reject_rhsbl_sender or reject_rhsbl_recipient
      restriction.

  

  
The numerical Postfix SMTP server reply code when a client request is
      rejected by the reject_non_fqdn_helo_hostname, reject_non_fqdn_sender or
      reject_non_fqdn_recipient restriction.

  

  
The numerical Postfix SMTP server response code when a request is rejected
      by the reject_plaintext_session restriction.

  

  
The numerical Postfix SMTP server response code when a remote SMTP client
      request is rejected by the "reject" restriction.

  

  
The numerical Postfix SMTP server response code when a client request is
      rejected by the reject_unauth_destination recipient restriction.

  

  
The numerical response code when the Postfix SMTP server rejects a sender
      or recipient address because its domain is unknown.

  

  
The numerical Postfix SMTP server response code when a client without
      valid address <=> name mapping is rejected by the
      reject_unknown_client_hostname restriction.

  

  
The numerical Postfix SMTP server response code when the hostname
      specified with the HELO or EHLO command is rejected by the
      reject_unknown_helo_hostname restriction.




Available in Postfix version 2.0 and later:



  

  
The default Postfix SMTP server response template for a request that is
      rejected by an RBL-based restriction.

  

  
The numerical Postfix SMTP server response code when a remote SMTP client
      request is blocked by the reject_multi_recipient_bounce restriction.

  

  
Optional lookup tables with RBL response templates.




Available in Postfix version 2.6 and later:



  

  
The numerical Postfix SMTP server response code for an access(5)
      map "defer" action, including "defer_if_permit" or
      "defer_if_reject".

  

  
The Postfix SMTP server's action when a reject-type restriction fails due
      to a temporary error condition.

  

  
The Postfix SMTP server's action when reject_unknown_helo_hostname fails
      due to a temporary error condition.

  

  
The Postfix SMTP server's action when reject_unknown_sender_domain or
      reject_unknown_recipient_domain fail due to a temporary error
    condition.








MISCELLANEOUS CONTROLS





  

  
The default location of the Postfix main.cf and master.cf configuration
      files.

  

  
How much time a Postfix daemon process may take to handle a request before
      it is terminated by a built-in watchdog timer.

  

  
The location of all postfix administrative commands.

  

  
The sender address of postmaster notifications that are generated by the
      mail system.

  

  
The time limit for sending or receiving information over an internal
      communication channel.

  

  
The mail system name that is displayed in Received: headers, in the SMTP
      greeting banner, and in bounced mail.

  

  
The UNIX system account that owns the Postfix queue and most Postfix
      daemon processes.

  

  
The maximum amount of time that an idle Postfix daemon process waits for
      an incoming connection before terminating voluntarily.

  

  
The maximal number of incoming connections that a Postfix daemon process
      will service before terminating voluntarily.

  

  
The internet hostname of this mail system.

  

  
The list of "trusted" remote SMTP clients that have more
      privileges than "strangers".

  

  
The domain name that locally-posted mail appears to come from, and that
      locally posted mail is delivered to.

  

  
The process ID of a Postfix command or daemon process.

  

  
The process name of a Postfix command or daemon process.

  

  
The location of the Postfix top-level queue directory.

  

  
The set of characters that can separate an email address localpart, user
      name, or a .forward file name from its extension.

  

  
The text that follows the 220 status code in the SMTP greeting
    banner.

  

  
The syslog facility of Postfix logging.

  

  
A prefix that is prepended to the process name in syslog records, so that,
      for example, "smtpd" becomes "prefix/smtpd".




Available in Postfix version 2.2 and later:



  

  
List of commands that cause the Postfix SMTP server to immediately
      terminate the session with a 221 code.




Available in Postfix version 2.5 and later:



  

  
Enable logging of the remote SMTP client port in addition to the hostname
      and IP address.




Available in Postfix 3.3 and later:



  

  
The master.cf service name of a Postfix daemon process.




Available in Postfix 3.4 and later:



  
  
Lookup tables, indexed by the complete Postfix SMTP server 4xx or 5xx
      response, with reject footer templates.








SEE ALSO


anvil(8), connection/rate limiting
cleanup(8), message canonicalization
tlsmgr(8), TLS session and PRNG management
trivial-rewrite(8), address resolver
verify(8), address verification service
postconf(5), configuration parameters
master(5), generic daemon options
master(8), process manager
postlogd(8), Postfix logging
syslogd(8), system logging






README FILES




Use "postconf readme_directory" or
    "postconf html_directory" to locate this information.


ADDRESS_CLASS_README, blocking unknown hosted or relay recipients
ADDRESS_REWRITING_README, Postfix address manipulation
BDAT_README, Postfix CHUNKING support
FILTER_README, external after-queue content filter
LOCAL_RECIPIENT_README, blocking unknown local recipients
MILTER_README, before-queue mail filter applications
SMTPD_ACCESS_README, built-in access policies
SMTPD_POLICY_README, external policy server
SMTPD_PROXY_README, external before-queue content filter
SASL_README, Postfix SASL howto
TLS_README, Postfix STARTTLS howto
VERP_README, Postfix XVERP extension
XCLIENT_README, Postfix XCLIENT extension
XFORWARD_README, Postfix XFORWARD extension






LICENSE




The Secure Mailer license must be distributed with this
  software.






AUTHOR(S)


Wietse Venema
IBM T.J. Watson Research
P.O. Box 704
Yorktown Heights, NY 10598, USA
Wietse Venema
Google, Inc.
111 8th Avenue
New York, NY 10011, USA
SASL support originally by:
Till Franke
SuSE Rhein/Main AG
65760 Eschborn, Germany
TLS support originally by:
Lutz Jaenicke
BTU Cottbus
Allgemeine Elektrotechnik
Universitaetsplatz 3-4
D-03044 Cottbus, Germany
Revised TLS support by:
Victor Duchovni
Morgan Stanley