8.4 Rewrite Rules

Rewrite rules determine the following:

• How to rewrite the domain part of an address into its proper or desired format.

• To which channel the message should be enqueued after the address is rewritten.

Each rewrite rule consists of a pattern and a template. The pattern is a string to match against the domain part of an address. The template specifies the actions to take if the domain part matches the pattern. It consists of two things: 1) a set of instructions (that is, a string of control characters) specifying how the address should be rewritten and 2) the name of the channel to which the message shall be sent. After the address is rewritten, the message is enqueued to the destination channel for delivery to the intended recipient.

An example of a rewrite rule is shown below:

siroe.com $U%$D@tcp_siroe-daemon

siroe.com is the domain pattern. Any message with the address containing siroe.com will be rewritten as per the template instructions ($U%$D). $U specifies that the rewritten address use the same user name. % specifies that the rewritten address use the same domain separator. $D specifies that the rewritten address use the same domain name that was matched in the pattern. @tcp_siroe-daemon specifies that the message with its rewritten address be sent to the channel called tcp_siroe-daemon. See Chapter 11, Configuring Rewrite Rules for more details.

For more information about configuring rewrite rules, see 10.2 The MTA Configuration File and Chapter 11, Configuring Rewrite Rules