To use FEATURE(`mailertable'), you will have to create an external
database containing the routing information for various domains.
For example, a mailertable file in text format might be:
This should normally be stored in /etc/mail/mailertable. The actual
database version of the mailertable is built using:
makemap hash /etc/mail/mailertable < /etc/mail/mailertable
The semantics are simple. Any LHS entry that does not begin with
a dot matches the full host name indicated. LHS entries beginning
with a dot match anything ending with that domain name (including
the leading dot) -- that is, they can be thought of as having a
leading ".+" regular expression pattern for a non-empty sequence of
characters. Matching is done in order of most-to-least qualified
-- for example, even though ".my.domain" is listed first in the
above example, an entry of "uuhost1.my.domain" will match the second
entry since it is more explicit.
Note: e-mail to "email@example.com"
does not match any entry in the above table. You need to have
The RHS should always be a "mailer:host" pair. The mailer is the
configuration name of a mailer (that is, an M line in the
sendmail.cf file). The "host" will be the hostname passed to
that mailer. In domain-based matches (that is, those with leading
dots) the "%1" may be used to interpolate the wildcarded part of
the host name. For example, the first line above sends everything
addressed to "anything.my.domain" to that same host name, but using
the (presumably experimental) xnet mailer.
In some cases you may want to temporarily turn off MX records,
particularly on gateways. For example, you may want to MX
everything in a domain to one machine that then forwards it
directly. To do this, you might use the DNS configuration:
*.domain. IN MX 0 relay.machine
and on relay.machine use the mailertable:
The [square brackets] turn off MX records for this host only.
If you didn't do this, the mailertable would use the MX record
again, which would give you an MX loop. Note that the use of
wildcard MX records is almost always a bad idea. Please avoid
using them if possible.