Timeouts all have option names
Timeout.suboption. The recognized
suboptions, their default values, and the minimum values
allowed by RFC 1123 section 5.3.2 are:
- The time to wait for an SMTP connection to open
connect(2) system call)
If zero, uses the kernel default.
In no case can this option extend the timeout
longer than the kernel provides, but it can shorten it.
This is to get around kernels that provide an absurdly long connection timeout
(90 minutes in one case).
- The wait for the initial 220 greeting message
- The wait for a reply from a HELO or EHLO command
This may require a host name lookup, so
five minutes is probably a reasonable minimum.
- The wait for a reply from a MAIL command
- The wait for a reply from a RCPT command
This should be long
because it could be pointing at a list
that takes a long time to expand
- The wait for a reply from a DATA command
- The wait for reading a data block
(that is, the body of the message).
This should be long because it also applies to programs
piping input to
sendmail which have no guarantee of promptness.
- The wait for a reply from the dot terminating a message.
If this is shorter than the time actually needed
for the receiver to deliver the message,
duplicates will be generated.
This is discussed in RFC 1047.
- The wait for a reply from a RSET command
- The wait for a reply from a QUIT command
- The wait for a reply from miscellaneous (but short) commands
such as NOOP (no-operation) and VERB (go into verbose mode).
- In server SMTP,
the time to wait for another command.
- The timeout waiting for a reply to an IDENT query
For compatibility with old configuration files,
suboption is specified,
all the timeouts marked with * are set to the indicated value.
Many of the RFC 1123 minimum values
may well be too short.
Sendmail was designed to the RFC 822 protocols,
which did not specify read timeouts;
hence, versions of
sendmail prior to version 8.1 did not guarantee to reply to messages promptly.
In particular, a
RCPT command specifying a mailing list
will expand and verify the entire list;
a large list on a slow system
may easily take more than five minutes.
I recommend a one hour timeout --
since a communications failure during the RCPT phase is rare,
a long timeout is not onerous
and may ultimately help reduce network load
and duplicated messages.
For example, the lines:
sets the server SMTP command timeout to 25 minutes
and the input data block timeout to three hours.
- O Timeout.command=25m
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Last modified: Friday April 02, 1999.