.TH SMTP 8 
.ad
.fi
.SH NAME
smtp
\-
Postfix remote delivery via SMTP
.SH SYNOPSIS
.na
.nf
\fBsmtp\fR [generic Postfix daemon options]
.SH DESCRIPTION
.ad
.fi
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 recipient information.
This program expects to be run from the \fBmaster\fR(8) process
manager.

The SMTP 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 problem reports are sent
to the \fBbounce\fR(8) or \fBdefer\fR(8) daemon 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 banner, 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.
.SH SECURITY
.na
.nf
.ad
.fi
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.
.SH STANDARDS
.na
.nf
RFC 821 (SMTP protocol)
RFC 1651 (SMTP service extensions)
RFC 1870 (Message Size Declaration)
RFC 2197 (Pipelining)
.SH DIAGNOSTICS
.ad
.fi
Problems and transactions are logged to \fBsyslogd\fR(8).
Corrupted message files are marked so that the queue manager can
move them to the \fBcorrupt\fR queue for further inspection.

Depending on the setting of the \fBnotify_classes\fR parameter,
the postmaster is notified of bounces, protocol problems, and of
other trouble.
.SH BUGS
.ad
.fi
.SH CONFIGURATION PARAMETERS
.na
.nf
.ad
.fi
The following \fBmain.cf\fR parameters are especially relevant to
this program. See the Postfix \fBmain.cf\fR file for syntax details
and for default values. Use the \fBpostfix reload\fR command after
a configuration change.
.SH Miscellaneous
.ad
.fi
.IP \fBbest_mx_transport\fR
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).
.IP \fBdebug_peer_level\fR
Verbose logging level increment for hosts that match a
pattern in the \fBdebug_peer_list\fR parameter.
.IP \fBdebug_peer_list\fR
List of domain or network patterns. When a remote host matches
a pattern, increase the verbose logging level by the amount
specified in the \fBdebug_peer_level\fR parameter.
.IP \fBdisable_dns_lookups\fR
Disable DNS lookups. This means that mail must be forwarded
via a smart relay host.
.IP \fBerror_notice_recipient\fR
Recipient of protocol/policy/resource/software error notices.
.IP \fBfallback_relay\fR
Hosts to hand off mail to if a message destination is not found
or if a destination is unreachable.
.IP \fBignore_mx_lookup_error\fR
When a name server fails to respond to an MX query, search for an
A record instead of assuming that the name server will recover.
.IP \fBinet_interfaces\fR
The network interface addresses that this mail system 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.
.IP \fBnotify_classes\fR
When this parameter includes the \fBprotocol\fR class, send mail to the
postmaster with transcripts of SMTP sessions with protocol errors.
.IP \fBsmtp_skip_4xx_greeting\fR
Skip servers that greet us with a 4xx status code.
.IP \fBsmtp_skip_quit_response\fR
Do not wait for the server response after sending QUIT.
.SH "Resource controls"
.ad
.fi
.IP \fBsmtp_destination_concurrency_limit\fR
Limit the number of parallel deliveries to the same destination.
The default limit is taken from the
\fBdefault_destination_concurrency_limit\fR parameter.
.IP \fBsmtp_destination_recipient_limit\fR
Limit the number of recipients per message delivery.
The default limit is taken from the
\fBdefault_destination_recipient_limit\fR parameter.
.SH "Timeout controls"
.ad
.fi
.IP \fBsmtp_connect_timeout\fR
Timeout in seconds 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.
.IP \fBsmtp_helo_timeout\fR
Timeout in seconds for receiving the SMTP greeting banner.
When the server drops the connection without sending 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.
.IP \fBsmtp_helo_timeout\fR
Timeout in seconds for sending the \fBHELO\fR command, and for
receiving the server response.
.IP \fBsmtp_mail_timeout\fR
Timeout in seconds for sending the \fBMAIL FROM\fR command, and for
receiving the server response.
.IP \fBsmtp_rcpt_timeout\fR
Timeout in seconds for sending the \fBRCPT TO\fR command, and for
receiving the server response.
.IP \fBsmtp_data_init_timeout\fR
Timeout in seconds for sending the \fBDATA\fR command, and for
receiving the server response.
.IP \fBsmtp_data_xfer_timeout\fR
Timeout in seconds for sending the message content.
.IP \fBsmtp_data_done_timeout\fR
Timeout in seconds for sending the "\fB.\fR" command, and for
receiving the server response. When no response is received, a
warning is logged that the mail may be delivered multiple times.
.IP \fBsmtp_quit_timeout\fR
Timeout in seconds for sending the \fBQUIT\fR command, and for
receiving the server response.
.SH SEE ALSO
.na
.nf
bounce(8) non-delivery status reports
master(8) process manager
qmgr(8) queue manager
syslogd(8) system logging
.SH LICENSE
.na
.nf
.ad
.fi
The Secure Mailer license must be distributed with this software.
.SH AUTHOR(S)
.na
.nf
Wietse Venema
IBM T.J. Watson Research
P.O. Box 704
Yorktown Heights, NY 10598, USA