Delivery Mode

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.