sendmail administration

Setting the delivery mode

There are a number of delivery modes for sendmail set by the DeliveryMode (d) configuration option. These modes specify how quickly mail is delivered. Legal modes are:

i: deliver interactively (synchronously)
b: deliver in background (asynchronously)
q: queue only (do not deliver)
d: defer delivery attempts (do not deliver)

There are tradeoffs. Mode ``i'' passes the maximum amount of information to the sender, but it is hardly ever necessary. Mode ``q'' puts the minimum load on your machine, but means that delivery may be delayed for up to the queue interval. Mode ``b'' delivers promptly and is probably a good compromise. However, this mode can cause large numbers of processes if you have a mailer that takes a long time to deliver a message. 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 (such as host unknown during the SMTP protocol) will be delayed using this mode. Mode "b" is the usual default.

If you run in mode ``q,'' ``d,'' or ``b,'' 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.