sendmail, 4th Edition

FEATURE(mailertable)

Database selects new delivery agents V8.1 and later

A mailertable is a database that maps host.domain names to special delivery agent and new domain name pairs. Essentially, it provides a database hook into the parse rule set 0. Because mailertable follows handling of the local host, none of the hosts in the $=w ($=w on page 876) will be looked up with this feature.

New domain names that result from a mailertable lookup are used for routing but are not reflected in the headers of messages.

To illustrate, one mapping in a source text file could look like this:

compuserv.com    smtp:compuserve.com

The key portion (on the left) must be either a fully qualified host and domain name, such as lady.bcx.com, or a partial domain specification with a leading dot, such as .bcx.com. On the right, the delivery agent name must be separated from the new domain name by a colon. The source text file is converted into a database with the makemap(1) program (The makemap Program on page 370). Beginning with V8.8 sendmail, the host part of the return value can also specify a user:

downhost.com     smtp:[e-mail]
                          ↑
                     V8.8 and later

The host.domain is looked up in the mailertable database, and if that host.domain is found, a delivery agent, colon, and domain pair are returned. If the delivery agent (in mailertable) is error, the #error delivery agent is called. This allows error messages to be put into the database, as, for example:

badhost error:nohost mail to badhost is prohibited ...