    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 manager. 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 connect 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 formatted 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, con-
                  nect to the port defined as  lmtp  in  services(4).
                  If no such service is found, the lmtp_tcp_port con-
                  figuration 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)

    DIAGNOSTICS
           Problems  and transactions are logged to syslogd(8).  Cor-
           rupted 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  postmaster 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 creden-
           tials 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 con-
           nections 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" parameter 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 Post-
                  fix  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 sta-
                  tus code.

           smtp_skip_quit_response (yes)
                  Do  not wait for the response to the SMTP QUIT com-
                  mand.

           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  key-
                  words  (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 (pipelin-
                  ing, 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 rewrit-
                  ing in the Postfix SMTP client, typically to trans-
                  form 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)
                  Allow  DNS CNAME records to override the servername
                  that the Postfix SMTP client uses for logging, SASL
                  password  lookup, TLS policy decisions, or TLS cer-
                  tificate 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 key-
                  words (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  (pipelin-
                  ing,  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  autho-
                  riZation ID (authzid); send only the SASL authenti-
                  Cation ID (authcid) plus the authcid'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 scaling.

           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 lim-
                  its, 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.

    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  XFOR-
                  WARD 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
                  username:password  entry  per  remote  hostname  or
                  domain, or  sender  address  when  sender-dependent
                  authentication is enabled.

           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 implementation 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 mecha-
                  nisms.

           Available in Postfix version 2.3 and later:

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

           smtp_sasl_path (empty)
                  Implementation-specific information that the  Post-
                  fix  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  authen-
                  tication  failures 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 authenti-
                  cation request with a 535 reply  code,  defer  mail
                  delivery  instead  of  returning mail as undeliver-
                  able.

           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_secu-
           rity_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  hand-
                  shake procedures.

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

           smtp_tls_CApath (empty)
                  Directory  with  PEM  format  certificate 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 levels.

           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  specified, this overrides the
                  obsolete smtp_tls_per_site parameter.

           smtp_tls_mandatory_protocols (!SSLv2)
                  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 cer-
                  tificates.

           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 ses-
                  sion 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
           (ALL:!EXPORT:!LOW:!MEDIUM:+RC4:@STRENGTH)
                  The OpenSSL cipherlist for "HIGH" grade ciphers.

           tls_medium_cipherlist (ALL:!EXPORT:!LOW:+RC4:@STRENGTH)
                  The OpenSSL cipherlist for "MEDIUM" or higher grade
                  ciphers.

           tls_low_cipherlist (ALL:!EXPORT:+RC4:@STRENGTH)
                  The OpenSSL cipherlist for "LOW"  or  higher  grade
                  ciphers.

           tls_export_cipherlist (ALL:+RC4:@STRENGTH)
                  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_security_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_security_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)
                  List of TLS protocols that the Postfix SMTP  client
                  will  exclude  or  include  with  opportunistic TLS
                  encryption.

           smtp_tls_ciphers (export)
                  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 format.

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

           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 malicious  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_dane_notfound_tlsa_level (may)
                  The "degraded" security level when the "dane" secu-
                  rity level is specified, but no validated DANE TLSA
                  records are published.

           smtp_tls_dane_unusable_tlsa_level (encrypt)
                  The "degraded" security level when the "dane" secu-
                  rity   level  is  specified,  validated  DANE  TLSA
                  records are present, but none are usable.

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

           tlsmgr_service_name (tlsmgr)
                  The  name  of  the  tlsmgr(8) service entry in mas-
                  ter.cf.

    OBSOLETE STARTTLS CONTROLS
           The following configuration parameters exist for  compati-
           bility 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 hostname.

           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_destina-
           tion_concurrency_limit)
                  The  maximal  number  of parallel deliveries to the
                  same destination  via  the  smtp  message  delivery
                  transport.

           smtp_destination_recipient_limit        ($default_destina-
           tion_recipient_limit)
                  The  maximal  number  of recipients per message for
                  the smtp message delivery transport.

           smtp_connect_timeout (30s)
                  The Postfix SMTP client time limit for completing a
                  TCP  connection,  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 command, 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 connection 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 operations.

           Available in Postfix version 2.9 and later:

           smtp_per_record_deadline (no)
                  Change the behavior of the smtp_*_timeout time lim-
                  its,  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).

    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 protocol errors.

           internal_mail_filter_classes (empty)
                  What categories of Postfix-generated mail are  sub-
                  ject   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 configuration 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 logging 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 sys-
                  tem 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"  delivery  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  termi-
                  nating 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 sys-
                  tem 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 destina-
                  tion  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 EHLO or HELO  com-
                  mand.

           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, "postfix/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.

    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

           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)