There are a number of delivery modes that
sendmail can operate in,
set by the
DeliveryMode (
d) configuration option.
These modes
specify how quickly mail will be delivered.
Legal modes are:
i deliver interactively (synchronously)
b deliver in background (asynchronously)
q queue only (don't deliver)
d defer delvery attempts (don't deliver)
There are tradeoffs.
Mode
i gives the sender the quickest feedback,
but may slow down some mailers and
is hardly ever necessary.
Mode
b delivers promptly but
can cause large numbers of processes
if you have a mailer that takes a long time to deliver a message.
Mode
q minimizes the load on your machine,
but means that delivery may be delayed for up to the queue interval.
Mode
d is identical to mode
q except that it also prevents all the early map lookups from working;
it is intended for ``dial on demand'' sites where DNS lookups
might cost real money.
Some simple error messages
(e.g., host unknown during the SMTP protocol)
will be delayed using this mode.
Mode
b is the usual default.
If you run in mode
q (queue only),
d (defer),
or
b (deliver in background)
sendmail will not expand aliases and follow .forward files
upon initial receipt of the mail.
This speeds up the response to RCPT commands.
Mode
i cannot be used by the SMTP server.
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Last modified: Friday April 02, 1999.