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 1651 (SMTP service extensions)
RFC 1870 (Message Size Declaration)
RFC 2197 (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
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SMTP(8) SMTP(8)
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.
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 assuming that the
name server will recover.
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.
notify_classes
When this parameter includes the protocol class,
send mail to the postmaster with transcripts of
SMTP sessions with protocol errors.
smtp_skip_4xx_greeting
Skip servers that greet us with a 4xx status code.
smtp_skip_quit_response
Do not wait for the server response after sending
QUIT.
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SMTP(8) SMTP(8)
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.
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.
Timeout controls
smtp_connect_timeout
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.
smtp_helo_timeout
Timeout in seconds for receiving the SMTP greeting
banner. When the server drops the connection with-
out 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.
smtp_helo_timeout
Timeout in seconds for sending the HELO command,
and for receiving the server response.
smtp_mail_timeout
Timeout in seconds for sending the MAIL FROM com-
mand, and for receiving the server response.
smtp_rcpt_timeout
Timeout in seconds for sending the RCPT TO command,
and for receiving the server response.
smtp_data_init_timeout
Timeout in seconds for sending the DATA command,
and for receiving the server response.
smtp_data_xfer_timeout
Timeout in seconds for sending the message content.
smtp_data_done_timeout
Timeout in seconds 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_quit_timeout
Timeout in seconds for sending the QUIT command,
and for receiving the server response.
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SMTP(8) SMTP(8)
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
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