Postfix manual - smtp(8)

    SMTP(8)                                                                SMTP(8)

    NAME
           smtp - Postfix SMTP+LMTP client

    SYNOPSIS
           smtp [generic Postfix daemon options]

    DESCRIPTION
           The Postfix SMTP+LMTP client implements the SMTP and LMTP mail delivery
           protocols. It processes message delivery requests from the  queue  man-
           ager.  Each  request specifies a queue file, a sender address, a domain
           or host to deliver to, and recipient information.  This program expects
           to be run from the master(8) process manager.

           The  SMTP+LMTP  client  updates  the queue file and marks recipients as
           finished, or it informs the queue manager that delivery should be tried
           again  at  a  later  time.  Delivery  status  reports  are  sent to the
           bounce(8), defer(8) or trace(8) daemon as appropriate.

           The SMTP+LMTP client looks up a list of mail  exchanger  addresses  for
           the  destination  host,  sorts  the list by preference, and connects to
           each listed address until it finds a server that responds.

           When a server is not reachable, or when mail delivery fails  due  to  a
           recoverable  error  condition, the SMTP+LMTP client will try to deliver
           the mail to an alternate host.

           After a successful mail transaction, a connection may be saved  to  the
           scache(8)  connection  cache  server,  so  that  it  may be used by any
           SMTP+LMTP client for a subsequent transaction.

           By default, connection caching is enabled temporarily for  destinations
           that have a high volume of mail in the active queue. Connection caching
           can be enabled permanently for specific destinations.

    SMTP DESTINATION SYNTAX
           SMTP destinations have the following form:

           domainname

           domainname:port
                  Look up the mail exchangers for the specified domain,  and  con-
                  nect to the specified port (default: smtp).

           [hostname]

           [hostname]:port
                  Look  up  the  address(es) of the specified host, and connect to
                  the specified port (default: smtp).

           [address]

           [address]:port
                  Connect to the host at the specified address, and connect to the
                  specified  port (default: smtp). An IPv6 address must be format-
                  ted as [ipv6:address].

    LMTP DESTINATION SYNTAX
           LMTP destinations have the following form:

           unix:pathname
                  Connect to the local UNIX-domain server that  is  bound  to  the
                  specified  pathname.  If  the process runs chrooted, an absolute
                  pathname is interpreted relative to the Postfix queue directory.

           inet:hostname

           inet:hostname:port

           inet:[address]

           inet:[address]:port
                  Connect  to  the  specified  TCP  port on the specified local or
                  remote host. If no  port  is  specified,  connect  to  the  port
                  defined  as  lmtp  in services(4).  If no such service is found,
                  the lmtp_tcp_port configuration parameter (default value of  24)
                  will   be   used.    An   IPv6  address  must  be  formatted  as
                  [ipv6:address].

    SECURITY
           The SMTP+LMTP client is moderately security-sensitive. It talks to SMTP
           or LMTP servers and to DNS servers on the network. The SMTP+LMTP client
           can be run chrooted at fixed low privilege.

    STANDARDS
           RFC 821 (SMTP protocol)
           RFC 822 (ARPA Internet Text Messages)
           RFC 1651 (SMTP service extensions)
           RFC 1652 (8bit-MIME transport)
           RFC 1870 (Message Size Declaration)
           RFC 2033 (LMTP protocol)
           RFC 2034 (SMTP Enhanced Error Codes)
           RFC 2045 (MIME: Format of Internet Message Bodies)
           RFC 2046 (MIME: Media Types)
           RFC 2554 (AUTH command)
           RFC 2821 (SMTP protocol)
           RFC 2920 (SMTP Pipelining)
           RFC 3207 (STARTTLS command)
           RFC 3461 (SMTP DSN Extension)
           RFC 3463 (Enhanced Status Codes)
           RFC 4954 (AUTH command)
           RFC 5321 (SMTP protocol)
           RFC 6531 (Internationalized SMTP)
           RFC 6533 (Internationalized Delivery Status Notifications)
           RFC 7672 (SMTP security via opportunistic DANE TLS)

    DIAGNOSTICS
           Problems and transactions are logged to syslogd(8).  Corrupted  message
           files are marked so that the queue manager can move them to the corrupt
           queue for further inspection.

           Depending on the setting of the notify_classes parameter, the  postmas-
           ter is notified of bounces, protocol problems, and of other trouble.

    BUGS
           SMTP  and LMTP connection caching does not work with TLS. The necessary
           support for TLS object passivation and  re-activation  does  not  exist
           without closing the session, which defeats the purpose.

           SMTP  and  LMTP  connection  caching  assumes that SASL credentials are
           valid for all destinations that map onto the same IP  address  and  TCP
           port.

    CONFIGURATION PARAMETERS
           Before  Postfix version 2.3, the LMTP client is a separate program that
           implements only a subset of  the  functionality  available  with  SMTP:
           there  is  no  support  for TLS, and connections are cached in-process,
           making it ineffective when the client is used for multiple domains.

           Most smtp_xxx configuration parameters have an lmtp_xxx "mirror" param-
           eter  for  the  equivalent  LMTP  feature. This document describes only
           those LMTP-related parameters that aren't simply "mirror" parameters.

           Changes to main.cf are picked up automatically,  as  smtp(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
           ignore_mx_lookup_error (no)
                  Ignore DNS MX lookups that produce no response.

           smtp_always_send_ehlo (yes)
                  Always send EHLO at the start of an SMTP session.

           smtp_never_send_ehlo (no)
                  Never send EHLO at the start of an SMTP session.

           smtp_defer_if_no_mx_address_found (no)
                  Defer mail delivery when no MX record resolves to an IP address.

           smtp_line_length_limit (998)
                  The maximal length of message header and body lines that Postfix
                  will send via SMTP.

           smtp_pix_workaround_delay_time (10s)
                  How   long   the  Postfix  SMTP  client  pauses  before  sending
                  ".<CR><LF>"  in  order  to  work   around   the   PIX   firewall
                  "<CR><LF>.<CR><LF>" bug.

           smtp_pix_workaround_threshold_time (500s)
                  How long a message must be queued before the Postfix SMTP client
                  turns on the PIX firewall "<CR><LF>.<CR><LF>" bug workaround for
                  delivery through firewalls with "smtp fixup" mode turned on.

           smtp_pix_workarounds (disable_esmtp, delay_dotcrlf)
                  A  list  that  specifies  zero or more workarounds for CISCO PIX
                  firewall bugs.

           smtp_pix_workaround_maps (empty)
                  Lookup tables, indexed by the remote SMTP server  address,  with
                  per-destination workarounds for CISCO PIX firewall bugs.

           smtp_quote_rfc821_envelope (yes)
                  Quote  addresses  in  Postfix  SMTP client MAIL FROM and RCPT TO
                  commands as required by RFC 5321.

           smtp_reply_filter (empty)
                  A mechanism to transform replies from remote  SMTP  servers  one
                  line at a time.

           smtp_skip_5xx_greeting (yes)
                  Skip remote SMTP servers that greet with a 5XX status code.

           smtp_skip_quit_response (yes)
                  Do not wait for the response to the SMTP QUIT command.

           Available in Postfix version 2.0 and earlier:

           smtp_skip_4xx_greeting (yes)
                  Skip  SMTP  servers  that greet with a 4XX status code (go away,
                  try again later).

           Available in Postfix version 2.2 and later:

           smtp_discard_ehlo_keyword_address_maps (empty)
                  Lookup tables, indexed by the remote SMTP server  address,  with
                  case  insensitive  lists of EHLO keywords (pipelining, starttls,
                  auth, etc.) that the Postfix SMTP client will ignore in the EHLO
                  response from a remote SMTP server.

           smtp_discard_ehlo_keywords (empty)
                  A  case insensitive list of EHLO keywords (pipelining, starttls,
                  auth, etc.) that the Postfix SMTP client will ignore in the EHLO
                  response from a remote SMTP server.

           smtp_generic_maps (empty)
                  Optional  lookup  tables  that  perform address rewriting in the
                  Postfix SMTP client, typically  to  transform  a  locally  valid
                  address  into  a globally valid address when sending mail across
                  the Internet.

           Available in Postfix version 2.2.9 and later:

           smtp_cname_overrides_servername (version dependent)
                  When the remote SMTP servername is  a  DNS  CNAME,  replace  the
                  servername  with the result from CNAME expansion for the purpose
                  of logging, SASL password lookup, TLS policy decisions,  or  TLS
                  certificate verification.

           Available in Postfix version 2.3 and later:

           lmtp_discard_lhlo_keyword_address_maps (empty)
                  Lookup  tables,  indexed by the remote LMTP server address, with
                  case insensitive lists of LHLO keywords  (pipelining,  starttls,
                  auth, etc.) that the Postfix LMTP client will ignore in the LHLO
                  response from a remote LMTP server.

           lmtp_discard_lhlo_keywords (empty)
                  A case insensitive list of LHLO keywords (pipelining,  starttls,
                  auth, etc.) that the Postfix LMTP client will ignore in the LHLO
                  response from a remote LMTP server.

           Available in Postfix version 2.4.4 and later:

           send_cyrus_sasl_authzid (no)
                  When authenticating to a remote SMTP or  LMTP  server  with  the
                  default  setting  "no", send no SASL authoriZation ID (authzid);
                  send only the SASL authentiCation ID (authcid)  plus  the  auth-
                  cid's password.

           Available in Postfix version 2.5 and later:

           smtp_header_checks (empty)
                  Restricted  header_checks(5) tables for the Postfix SMTP client.

           smtp_mime_header_checks (empty)
                  Restricted mime_header_checks(5) tables  for  the  Postfix  SMTP
                  client.

           smtp_nested_header_checks (empty)
                  Restricted  nested_header_checks(5)  tables for the Postfix SMTP
                  client.

           smtp_body_checks (empty)
                  Restricted body_checks(5) tables for the Postfix SMTP client.

           Available in Postfix version 2.6 and later:

           tcp_windowsize (0)
                  An optional workaround for routers that break TCP  window  scal-
                  ing.

           Available in Postfix version 2.8 and later:

           smtp_dns_resolver_options (empty)
                  DNS Resolver options for the Postfix SMTP client.

           Available in Postfix version 2.9 and later:

           smtp_per_record_deadline (no)
                  Change  the  behavior  of the smtp_*_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  mes-
                  sage).

           smtp_send_dummy_mail_auth (no)
                  Whether  or  not to append the "AUTH=<>" option to the MAIL FROM
                  command in SASL-authenticated SMTP sessions.

           Available in Postfix version 2.11 and later:

           smtp_dns_support_level (empty)
                  Level of DNS support in the Postfix SMTP client.

           Available in Postfix version 3.0 and later:

           smtp_delivery_status_filter ($default_delivery_status_filter)
                  Optional filter for the smtp(8) delivery  agent  to  change  the
                  delivery status code or explanatory text of successful or unsuc-
                  cessful deliveries.

           smtp_dns_reply_filter (empty)
                  Optional filter for Postfix SMTP client DNS lookup results.

    MIME PROCESSING CONTROLS
           Available in Postfix version 2.0 and later:

           disable_mime_output_conversion (no)
                  Disable the conversion of 8BITMIME format to 7BIT format.

           mime_boundary_length_limit (2048)
                  The maximal length of MIME multipart boundary strings.

           mime_nesting_limit (100)
                  The maximal recursion level that the MIME processor will handle.

    EXTERNAL CONTENT INSPECTION CONTROLS
           Available in Postfix version 2.1 and later:

           smtp_send_xforward_command (no)
                  Send  the  non-standard  XFORWARD  command when the Postfix SMTP
                  server EHLO response announces XFORWARD support.

    SASL AUTHENTICATION CONTROLS
           smtp_sasl_auth_enable (no)
                  Enable SASL authentication in the Postfix SMTP client.

           smtp_sasl_password_maps (empty)
                  Optional Postfix  SMTP  client  lookup  tables  with  one  user-
                  name:password  entry  per  sender,  remote  hostname or next-hop
                  domain.

           smtp_sasl_security_options (noplaintext, noanonymous)
                  Postfix SMTP client SASL security options; as of Postfix 2.3 the
                  list  of available features depends on the SASL client implemen-
                  tation that is selected with smtp_sasl_type.

           Available in Postfix version 2.2 and later:

           smtp_sasl_mechanism_filter (empty)
                  If non-empty, a Postfix SMTP client filter for the  remote  SMTP
                  server's list of offered SASL mechanisms.

           Available in Postfix version 2.3 and later:

           smtp_sender_dependent_authentication (no)
                  Enable  sender-dependent  authentication  in  the  Postfix  SMTP
                  client; this is available only  with  SASL  authentication,  and
                  disables  SMTP  connection caching to ensure that mail from dif-
                  ferent senders will use the appropriate credentials.

           smtp_sasl_path (empty)
                  Implementation-specific information that the Postfix SMTP client
                  passes  through  to  the  SASL  plug-in  implementation  that is
                  selected with smtp_sasl_type.

           smtp_sasl_type (cyrus)
                  The SASL plug-in type that the Postfix SMTP  client  should  use
                  for authentication.

           Available in Postfix version 2.5 and later:

           smtp_sasl_auth_cache_name (empty)
                  An  optional table to prevent repeated SASL authentication fail-
                  ures with the same remote SMTP  server  hostname,  username  and
                  password.

           smtp_sasl_auth_cache_time (90d)
                  The  maximal age of an smtp_sasl_auth_cache_name entry before it
                  is removed.

           smtp_sasl_auth_soft_bounce (yes)
                  When a remote SMTP server rejects a SASL authentication  request
                  with  a 535 reply code, defer mail delivery instead of returning
                  mail as undeliverable.

           Available in Postfix version 2.9 and later:

           smtp_send_dummy_mail_auth (no)
                  Whether or not to append the "AUTH=<>" option to the  MAIL  FROM
                  command in SASL-authenticated SMTP sessions.

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

           smtp_tls_security_level (empty)
                  The default SMTP TLS security level for the Postfix SMTP client;
                  when a non-empty value is specified, this overrides the obsolete
                  parameters       smtp_use_tls,       smtp_enforce_tls,       and
                  smtp_tls_enforce_peername.

           smtp_sasl_tls_security_options ($smtp_sasl_security_options)
                  The  SASL  authentication security options that the Postfix SMTP
                  client uses for TLS encrypted SMTP sessions.

           smtp_starttls_timeout (300s)
                  Time limit for Postfix SMTP client  write  and  read  operations
                  during TLS startup and shutdown handshake procedures.

           smtp_tls_CAfile (empty)
                  A  file  containing  CA certificates of root CAs trusted to sign
                  either remote SMTP server certificates or intermediate  CA  cer-
                  tificates.

           smtp_tls_CApath (empty)
                  Directory  with  PEM format Certification Authority certificates
                  that the Postfix SMTP client uses to verify a remote SMTP server
                  certificate.

           smtp_tls_cert_file (empty)
                  File with the Postfix SMTP client RSA certificate in PEM format.

           smtp_tls_mandatory_ciphers (medium)
                  The minimum TLS cipher grade that the Postfix SMTP  client  will
                  use with mandatory TLS encryption.

           smtp_tls_exclude_ciphers (empty)
                  List of ciphers or cipher types to exclude from the Postfix SMTP
                  client cipher list at all TLS security levels.

           smtp_tls_mandatory_exclude_ciphers (empty)
                  Additional list of ciphers or cipher types to exclude  from  the
                  Postfix  SMTP  client cipher list at mandatory TLS security lev-
                  els.

           smtp_tls_dcert_file (empty)
                  File with the Postfix SMTP client DSA certificate in PEM format.

           smtp_tls_dkey_file ($smtp_tls_dcert_file)
                  File with the Postfix SMTP client DSA private key in PEM format.

           smtp_tls_key_file ($smtp_tls_cert_file)
                  File with the Postfix SMTP client RSA private key in PEM format.

           smtp_tls_loglevel (0)
                  Enable additional Postfix SMTP client logging of TLS activity.

           smtp_tls_note_starttls_offer (no)
                  Log  the  hostname of a remote SMTP server that offers STARTTLS,
                  when TLS is not already enabled for that server.

           smtp_tls_policy_maps (empty)
                  Optional lookup tables with the Postfix SMTP client TLS security
                  policy by next-hop destination; when a non-empty value is speci-
                  fied, this overrides the obsolete smtp_tls_per_site parameter.

           smtp_tls_mandatory_protocols (!SSLv2, !SSLv3)
                  List of SSL/TLS protocols that the Postfix SMTP client will  use
                  with mandatory TLS encryption.

           smtp_tls_scert_verifydepth (9)
                  The verification depth for remote SMTP server certificates.

           smtp_tls_secure_cert_match (nexthop, dot-nexthop)
                  How  the  Postfix  SMTP  client  verifies the server certificate
                  peername for the "secure" TLS security level.

           smtp_tls_session_cache_database (empty)
                  Name of the file containing the optional Postfix SMTP client TLS
                  session cache.

           smtp_tls_session_cache_timeout (3600s)
                  The  expiration  time  of  Postfix SMTP client TLS session cache
                  information.

           smtp_tls_verify_cert_match (hostname)
                  How the Postfix SMTP  client  verifies  the  server  certificate
                  peername for the "verify" TLS security level.

           tls_daemon_random_bytes (32)
                  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).

           tls_high_cipherlist (see 'postconf -d' output)
                  The OpenSSL cipherlist for "high" grade ciphers.

           tls_medium_cipherlist (see 'postconf -d' output)
                  The OpenSSL cipherlist for "medium" or higher grade ciphers.

           tls_low_cipherlist (see 'postconf -d' output)
                  The OpenSSL cipherlist for "low" or higher grade ciphers.

           tls_export_cipherlist (see 'postconf -d' output)
                  The OpenSSL cipherlist for "export" or higher grade ciphers.

           tls_null_cipherlist (eNULL:!aNULL)
                  The  OpenSSL  cipherlist  for  "NULL" grade ciphers that provide
                  authentication without encryption.

           Available in Postfix version 2.4 and later:

           smtp_sasl_tls_verified_security_options           ($smtp_sasl_tls_secu-
           rity_options)
                  The SASL authentication security options that the  Postfix  SMTP
                  client  uses  for  TLS  encrypted  SMTP sessions with a verified
                  server certificate.

           Available in Postfix version 2.5 and later:

           smtp_tls_fingerprint_cert_match (empty)
                  List of acceptable remote SMTP server  certificate  fingerprints
                  for   the   "fingerprint"  TLS  security  level  (smtp_tls_secu-
                  rity_level = fingerprint).

           smtp_tls_fingerprint_digest (md5)
                  The message digest  algorithm  used  to  construct  remote  SMTP
                  server certificate fingerprints.

           Available in Postfix version 2.6 and later:

           smtp_tls_protocols (!SSLv2, !SSLv3)
                  List  of TLS protocols that the Postfix SMTP client will exclude
                  or include with opportunistic TLS encryption.

           smtp_tls_ciphers (medium)
                  The minimum TLS cipher grade that the Postfix SMTP  client  will
                  use with opportunistic TLS encryption.

           smtp_tls_eccert_file (empty)
                  File  with the Postfix SMTP client ECDSA certificate in PEM for-
                  mat.

           smtp_tls_eckey_file ($smtp_tls_eccert_file)
                  File with the Postfix SMTP client ECDSA private key in PEM  for-
                  mat.

           Available in Postfix version 2.7 and later:

           smtp_tls_block_early_mail_reply (no)
                  Try  to  detect  a mail hijacking attack based on a TLS protocol
                  vulnerability (CVE-2009-3555), where an attacker prepends  mali-
                  cious  HELO,  MAIL, RCPT, DATA commands to a Postfix SMTP client
                  TLS session.

           Available in Postfix version 2.8 and later:

           tls_disable_workarounds (see 'postconf -d' output)
                  List or bit-mask of OpenSSL bug work-arounds to disable.

           Available in Postfix version 2.11 and later:

           smtp_tls_trust_anchor_file (empty)
                  Zero or more PEM-format  files  with  trust-anchor  certificates
                  and/or public keys.

           smtp_tls_force_insecure_host_tlsa_lookup (no)
                  Lookup  the  associated  DANE TLSA RRset even when a hostname is
                  not an alias and its address records lie in an unsigned zone.

           tls_dane_trust_anchor_digest_enable (yes)
                  RFC 6698 trust-anchor digest support in the Postfix TLS library.

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

           Available in Postfix version 3.0 and later:

           smtp_tls_wrappermode (no)
                  Request  that  the Postfix SMTP client connects using the legacy
                  SMTPS protocol instead of using the STARTTLS command.

           Available in Postfix version 3.1 and later:

           smtp_tls_dane_insecure_mx_policy (dane)
                  The TLS policy for MX hosts with "secure" TLSA records when  the
                  nexthop  destination  security  level is dane, but the MX record
                  was found via an "insecure" MX lookup.

    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.

           smtp_use_tls (no)
                  Opportunistic mode: use TLS when a remote SMTP server  announces
                  STARTTLS support, otherwise send the mail in the clear.

           smtp_enforce_tls (no)
                  Enforcement  mode:  require  that  remote  SMTP  servers use TLS
                  encryption, and never send mail in the clear.

           smtp_tls_enforce_peername (yes)
                  With mandatory TLS encryption,  require  that  the  remote  SMTP
                  server  hostname  matches  the  information  in  the remote SMTP
                  server certificate.

           smtp_tls_per_site (empty)
                  Optional lookup tables with the Postfix SMTP  client  TLS  usage
                  policy  by  next-hop destination and by remote SMTP server host-
                  name.

           smtp_tls_cipherlist (empty)
                  Obsolete Postfix < 2.3 control for the Postfix SMTP  client  TLS
                  cipher list.

    RESOURCE AND RATE CONTROLS
           smtp_destination_concurrency_limit        ($default_destination_concur-
           rency_limit)
                  The  maximal  number of parallel deliveries to the same destina-
                  tion via the smtp message delivery transport.

           smtp_destination_recipient_limit ($default_destination_recipient_limit)
                  The maximal number of recipients per message for the  smtp  mes-
                  sage delivery transport.

           smtp_connect_timeout (30s)
                  The  Postfix SMTP client time limit for completing a TCP connec-
                  tion, or zero (use the operating system built-in time limit).

           smtp_helo_timeout (300s)
                  The Postfix SMTP client time limit for sending the HELO or  EHLO
                  command,  and  for  receiving  the  initial  remote  SMTP server
                  response.

           lmtp_lhlo_timeout (300s)
                  The Postfix LMTP client time limit for sending the LHLO command,
                  and for receiving the initial remote LMTP server response.

           smtp_xforward_timeout (300s)
                  The Postfix SMTP client time limit for sending the XFORWARD com-
                  mand, and for receiving the remote SMTP server response.

           smtp_mail_timeout (300s)
                  The Postfix SMTP client time limit for  sending  the  MAIL  FROM
                  command, and for receiving the remote SMTP server response.

           smtp_rcpt_timeout (300s)
                  The  Postfix SMTP client time limit for sending the SMTP RCPT TO
                  command, and for receiving the remote SMTP server response.

           smtp_data_init_timeout (120s)
                  The Postfix SMTP client time limit for  sending  the  SMTP  DATA
                  command, and for receiving the remote SMTP server response.

           smtp_data_xfer_timeout (180s)
                  The  Postfix SMTP client time limit for sending the SMTP message
                  content.

           smtp_data_done_timeout (600s)
                  The Postfix SMTP client time limit for sending the SMTP ".", and
                  for receiving the remote SMTP server response.

           smtp_quit_timeout (300s)
                  The Postfix SMTP client time limit for sending the QUIT command,
                  and for receiving the remote SMTP server response.

           Available in Postfix version 2.1 and later:

           smtp_mx_address_limit (5)
                  The maximal number of MX (mail exchanger) IP addresses that  can
                  result  from Postfix SMTP client mail exchanger lookups, or zero
                  (no limit).

           smtp_mx_session_limit (2)
                  The maximal number of SMTP sessions per delivery request  before
                  the  Postfix  SMTP  client  gives  up or delivers to a fall-back
                  relay host, or zero (no limit).

           smtp_rset_timeout (20s)
                  The Postfix SMTP client time limit for sending the RSET command,
                  and for receiving the remote SMTP server response.

           Available in Postfix version 2.2 and earlier:

           lmtp_cache_connection (yes)
                  Keep  Postfix  LMTP  client connections open for up to $max_idle
                  seconds.

           Available in Postfix version 2.2 and later:

           smtp_connection_cache_destinations (empty)
                  Permanently enable SMTP connection  caching  for  the  specified
                  destinations.

           smtp_connection_cache_on_demand (yes)
                  Temporarily  enable  SMTP connection caching while a destination
                  has a high volume of mail in the active queue.

           smtp_connection_reuse_time_limit (300s)
                  The amount of time during which Postfix will use an SMTP connec-
                  tion repeatedly.

           smtp_connection_cache_time_limit (2s)
                  When SMTP connection caching is enabled, the amount of time that
                  an unused SMTP client socket is kept open before it is closed.

           Available in Postfix version 2.3 and later:

           connection_cache_protocol_timeout (5s)
                  Time limit for connection cache connect, send or receive  opera-
                  tions.

           Available in Postfix version 2.9 and later:

           smtp_per_record_deadline (no)
                  Change  the  behavior  of the smtp_*_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  mes-
                  sage).

           Available in Postfix version 2.11 and later:

           smtp_connection_reuse_count_limit (0)
                  When  SMTP  connection  caching  is enabled, the number of times
                  that an SMTP session may be reused before it is closed, or  zero
                  (no limit).

    SMTPUTF8 CONTROLS
           Preliminary SMTPUTF8 support is introduced with Postfix 3.0.

           smtputf8_enable (yes)
                  Enable  preliminary SMTPUTF8 support for the protocols described
                  in RFC 6531..6533.

           smtputf8_autodetect_classes (sendmail, verify)
                  Detect that a message requires SMTPUTF8 support for  the  speci-
                  fied mail origin classes.

    TROUBLE SHOOTING CONTROLS
           debug_peer_level (2)
                  The  increment  in verbose logging level when a remote client or
                  server matches a pattern in the debug_peer_list parameter.

           debug_peer_list (empty)
                  Optional list of remote client or  server  hostname  or  network
                  address  patterns  that  cause  the  verbose  logging  level  to
                  increase by the amount specified in $debug_peer_level.

           error_notice_recipient (postmaster)
                  The recipient of postmaster notifications  about  mail  delivery
                  problems that are caused by policy, resource, software or proto-
                  col errors.

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

           notify_classes (resource, software)
                  The list of error classes that are reported to the postmaster.

    MISCELLANEOUS CONTROLS
           best_mx_transport (empty)
                  Where the Postfix  SMTP  client  should  deliver  mail  when  it
                  detects a "mail loops back to myself" error condition.

           config_directory (see 'postconf -d' output)
                  The  default  location of the Postfix main.cf and master.cf con-
                  figuration files.

           daemon_timeout (18000s)
                  How much time a Postfix daemon process  may  take  to  handle  a
                  request before it is terminated by a built-in watchdog timer.

           delay_logging_resolution_limit (2)
                  The  maximal  number of digits after the decimal point when log-
                  ging sub-second delay values.

           disable_dns_lookups (no)
                  Disable DNS lookups in the Postfix SMTP and LMTP clients.

           inet_interfaces (all)
                  The network interface addresses that this mail  system  receives
                  mail on.

           inet_protocols (all)
                  The  Internet  protocols Postfix will attempt to use when making
                  or accepting connections.

           ipc_timeout (3600s)
                  The time limit for sending  or  receiving  information  over  an
                  internal communication channel.

           lmtp_assume_final (no)
                  When  a remote LMTP server announces no DSN support, assume that
                  the server performs final delivery, and send "delivered"  deliv-
                  ery status notifications instead of "relayed".

           lmtp_tcp_port (24)
                  The default TCP port that the Postfix LMTP client connects to.

           max_idle (100s)
                  The  maximum  amount of time that an idle Postfix daemon process
                  waits for an incoming connection before terminating voluntarily.

           max_use (100)
                  The maximal number of incoming connections that a Postfix daemon
                  process will service before terminating voluntarily.

           process_id (read-only)
                  The process ID of a Postfix command or daemon process.

           process_name (read-only)
                  The process name of a Postfix command or daemon process.

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

           smtp_address_preference (any)
                  The address type ("ipv6", "ipv4" or "any") that the Postfix SMTP
                  client will try first, when a  destination  has  IPv6  and  IPv4
                  addresses with equal MX preference.

           smtp_bind_address (empty)
                  An  optional  numerical  network  address  that the Postfix SMTP
                  client should bind to when making an IPv4 connection.

           smtp_bind_address6 (empty)
                  An optional numerical network  address  that  the  Postfix  SMTP
                  client should bind to when making an IPv6 connection.

           smtp_helo_name ($myhostname)
                  The hostname to send in the SMTP HELO or EHLO command.

           lmtp_lhlo_name ($myhostname)
                  The hostname to send in the LMTP LHLO command.

           smtp_host_lookup (dns)
                  What mechanisms the Postfix SMTP client uses to look up a host's
                  IP address.

           smtp_randomize_addresses (yes)
                  Randomize the order of equal-preference MX host addresses.

           syslog_facility (mail)
                  The syslog facility of Postfix logging.

           syslog_name (see 'postconf -d' output)
                  The mail system name that is prepended to the  process  name  in
                  syslog  records,  so  that  "smtpd" becomes, for example, "post-
                  fix/smtpd".

           Available with Postfix 2.2 and earlier:

           fallback_relay (empty)
                  Optional list of relay hosts for SMTP destinations that can't be
                  found or that are unreachable.

           Available with Postfix 2.3 and later:

           smtp_fallback_relay ($fallback_relay)
                  Optional list of relay hosts for SMTP destinations that can't be
                  found or that are unreachable.

           Available with Postfix 3.0 and later:

           smtp_address_verify_target (rcpt)
                  In the context of email address verification, the SMTP  protocol
                  stage that determines whether an email address is deliverable.

           Available with Postfix 3.1 and later:

           lmtp_fallback_relay (empty)
                  Optional list of relay hosts for LMTP destinations that can't be
                  found or that are unreachable.

    SEE ALSO
           generic(5), output address rewriting
           header_checks(5), message header content inspection
           body_checks(5), body parts content inspection
           qmgr(8), queue manager
           bounce(8), delivery status reports
           scache(8), connection cache server
           postconf(5), configuration parameters
           master(5), generic daemon options
           master(8), process manager
           tlsmgr(8), TLS session and PRNG management
           syslogd(8), system logging

    README FILES
           SASL_README, Postfix SASL howto
           TLS_README, Postfix STARTTLS howto

    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

           Command pipelining in cooperation with:
           Jon Ribbens
           Oaktree Internet Solutions Ltd.,
           Internet House,
           Canal Basin,
           Coventry,
           CV1 4LY, United Kingdom.

           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 and SMTP connection cache support by:
           Victor Duchovni
           Morgan Stanley

                                                                           SMTP(8)