    SMTP(8)                                                   SMTP(8)

    NAME
           smtp - Postfix remote delivery via SMTP

    SYNOPSIS
           smtp [generic Postfix daemon options]

    DESCRIPTION
           The  SMTP  client 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 recip-
           ient information.  This program expects to be run from the
           master(8) process manager.

           The  SMTP  client updates the queue file and marks recipi-
           ents as finished, or it informs  the  queue  manager  that
           delivery  should  be tried again at a later time. Delivery
           problem reports are sent to the bounce(8) or defer(8) dae-
           mon as appropriate.

           The  SMTP  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.

           Once the SMTP client has received the server greeting ban-
           ner, no error will cause it to proceed to the next address
           on the mail exchanger list. Instead, the message is either
           bounced, or its delivery is deferred until later.

    SECURITY
           The SMTP client is moderately security-sensitive. It talks
           to SMTP servers and to DNS servers  on  the  network.  The
           SMTP 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 2045 (MIME: Format of Internet Message Bodies)
           RFC 2046 (MIME: Media Types)
           RFC 2554 (AUTH command)
           RFC 2821 (SMTP protocol)
           RFC 2920 (SMTP Pipelining)

    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
    CONFIGURATION PARAMETERS
           The following main.cf parameters are  especially  relevant
           to  this  program. See the Postfix main.cf file for syntax
           details and for default values.  Use  the  postfix  reload
           command after a configuration change.

    Miscellaneous
           best_mx_transport
                  Name  of  the  delivery  transport  to use when the
                  local machine is the most-preferred mail  exchanger
                  (by  default,  a  mailer  loop is reported, and the
                  message is bounced).

           debug_peer_level
                  Verbose logging  level  increment  for  hosts  that
                  match a pattern in the debug_peer_list parameter.

           debug_peer_list
                  List  of  domain or network patterns. When a remote
                  host matches a pattern, increase the  verbose  log-
                  ging   level   by   the  amount  specified  in  the
                  debug_peer_level parameter.

           disable_dns_lookups
                  Disable DNS lookups. This means that mail  must  be
                  forwarded via a smart relay host.

           smtp_host_lookup
                  What  host  lookup mechanism the SMTP client should
                  use.  Specify dns (use DNS  lookup)  and/or  native
                  (use  the  native  naming  service  which also uses
                  /etc/hosts).  This  setting  is  ignored  when  DNS
                  lookups are disabled.

           error_notice_recipient
                  Recipient    of   protocol/policy/resource/software
                  error notices.

           fallback_relay
                  Hosts to hand off mail to if a message  destination
                  is not found or if a destination is unreachable.

           ignore_mx_lookup_error
                  When a name server fails to respond to an MX query,
                  search for an A record, instead of  deferring  mail
                  delivery.

           inet_interfaces
                  The network interface addresses that this mail sys-
                  tem receives mail on. When any of  those  addresses
                  appears in the list of mail exchangers for a remote
                  destination, the list is truncated  to  avoid  mail
                  delivery  loops.   See  also  the  proxy_interfaces
                  parameter.

           notify_classes
                  When this parameter includes  the  protocol  class,
                  send  mail  to  the  postmaster with transcripts of
                  SMTP sessions with protocol errors.

           proxy_interfaces
                  Network interfaces that this mail  system  receives
                  mail on by way of a proxy or network address trans-
                  lator. When any of those addresses appears  in  the
                  list  of  mail exchangers for a remote destination,
                  the list is truncated to avoid mail delivery loops.
                  See also the inet_interfaces parameter.

           smtp_always_send_ehlo
                  Always send EHLO at the start of a connection.

           smtp_never_send_ehlo
                  Never send EHLO at the start of a connection.

           smtp_bind_address
                  Numerical  source  network  address to bind to when
                  making a connection.

           smtp_defer_if_no_mx_address_found
                  If no, bounce mail when no MX host resolves  to  an
                  address (Postfix always ignores MX hosts with equal
                  or worse preference than the local MTA).   If  yes,
                  keep  trying  until  a suitable MX host resolves or
                  until the mail is too old.

           smtp_line_length_limit
                  Length limit for SMTP message content  lines.  Zero
                  means  no  limit.   Some  SMTP servers misbehave on
                  long lines.

           smtp_helo_name
                  The hostname to be used in HELO and EHLO  commands.

           smtp_quote_rfc821_envelope
                  Whether  or  not  to  quote  MAIL  FROM and RCPT TO
                  addresses as per the rules laid out in RFC 821.

           smtp_skip_4xx_greeting
                  Skip servers that greet us with a 4xx status  code.

           smtp_skip_5xx_greeting
                  Skip  servers that greet us with a 5xx status code.

           smtp_skip_quit_response
                  Do not wait for the server response  after  sending
                  QUIT.

           smtp_pix_workaround_delay_time
                  The  time  to pause before sending .<CR><LF>, while
                  working   around    the    CISCO    PIX    firewall
                  <CR><LF>.<CR><LF> bug.

           smtp_pix_workaround_threshold_time
                  The  time a message must be queued before the CISCO
                  PIX firewall <CR><LF>.<CR><LF>  bug  workaround  is
                  turned on.

    MIME Conversion
           disable_mime_output_conversion
                  Disable  the  conversion of 8BITMIME format to 7BIT
                  format when the remote system  does  not  advertise
                  8BITMIME support.

           mime_boundary_length_limit
                  The amount of space that will be allocated for MIME
                  multipart boundary strings. The MIME  processor  is
                  unable to distinguish between boundary strings that
                  do   not   differ   in   the   first   $mime_bound-
                  ary_length_limit characters.

           mime_nesting_limit
                  The  maximal  nesting  level of multipart mail that
                  the MIME processor can handle. Refuse mail that  is
                  nested deeper, when converting from 8BITMIME format
                  to 7BIT format.

           smtp_send_xforward_command
                  If the SMTP server announces XFORWARD support, send
                  the  name,  address,  protocol and HELO name of the
                  original client. This can be used to forward client
                  information  through  a  content  filter to a down-
                  stream queuing SMTP server.

    Authentication controls
           smtp_sasl_auth_enable
                  Enable per-session authentication as per  RFC  2554
                  (SASL).   By default, Postfix is built without SASL
                  support.

           smtp_sasl_password_maps
                  Lookup tables with per-host or domain name:password
                  entries.   No  entry for a host means no attempt to
                  authenticate.

           smtp_sasl_security_options
                  Zero or more of the following.

                  noplaintext
                         Disallow  authentication  methods  that  use
                         plaintext passwords.

                  noactive
                         Disallow  authentication  methods  that  are
                         vulnerable to non-dictionary active attacks.

                  nodictionary
                         Disallow  authentication  methods  that  are
                         vulnerable to passive dictionary attack.

                  noanonymous
                         Disallow anonymous logins.

    Resource controls
           smtp_destination_concurrency_limit
                  Limit the number of parallel deliveries to the same
                  destination.   The  default limit is taken from the
                  default_destination_concurrency_limit parameter.

                  NB: This limit is enforced by the queue manager.

           smtp_destination_recipient_limit
                  Limit the number of recipients per  message  deliv-
                  ery.    The   default   limit  is  taken  from  the
                  default_destination_recipient_limit parameter.

           smtp_mx_address_limit
                  An upper bound on the  total  number  of  MX  (mail
                  exchanger)  IP  addresses that can result from mail
                  exchanger lookups.

                  Specify zero to disable the limit.

                  Note: by default, equal preference MX addresses are
                  sorted into random order.

           smtp_mx_session_limit
                  An  upper  bound on the number of SMTP sessions per
                  delivery request before giving up or delivering  to
                  a  fall-back relay host (ignoring IP addresses that
                  fail to complete the SMTP initial handshake).

                  Specify zero to disable the limit.

    Timeout controls
           The default time unit is seconds; an  explicit  time  unit
           can  be  specified by appending a one-letter suffix to the
           value: s (seconds), m (minutes), h (hours), d (days) or  w
           (weeks).

           smtp_connect_timeout
                  Timeout  for  completing  a TCP connection. When no
                  connection can be made  within  the  deadline,  the
                  SMTP  client  tries  the  next  address on the mail
                  exchanger list.

           smtp_helo_timeout
                  Timeout for receiving  the  SMTP  greeting  banner.
                  When  the server drops the connection without send-
                  ing a greeting banner, or when it sends no greeting
                  banner  within  the deadline, the SMTP client tries
                  the next address on the mail exchanger list.

           smtp_helo_timeout
                  Timeout for  sending  the  HELO  command,  and  for
                  receiving the server response.

           smtp_xforward_timeout
                  Timeout  for  sending the XFORWARD command, and for
                  receiving the server response.

           smtp_mail_timeout
                  Timeout for sending the MAIL FROM command, and  for
                  receiving the server response.

           smtp_rcpt_timeout
                  Timeout  for  sending  the RCPT TO command, and for
                  receiving the server response.

           smtp_data_init_timeout
                  Timeout for  sending  the  DATA  command,  and  for
                  receiving the server response.

           smtp_data_xfer_timeout
                  Timeout for sending the message content.

           smtp_data_done_timeout
                  Timeout  for  sending  the  "."  command,  and  for
                  receiving the server response. When no response  is
                  received,  a warning is logged that the mail may be
                  delivered multiple times.

           smtp_rset_timeout
                  Timeout for sending the RSET command.

           smtp_quit_timeout
                  Timeout for  sending  the  QUIT  command,  and  for
                  receiving the server response.

    SEE ALSO
           bounce(8) non-delivery status reports
           master(8) process manager
           qmgr(8) queue manager
           syslogd(8) system logging

    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

                                                              SMTP(8)