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630 | Chapter 17: Configure sendmail.cf with m4
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, th e#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 ?†? V8.9 and earlier
badhost error:5.7.0:550 mail to badhost is prohibited ?†? V8.10 and later
The first token following the error: is passed in the $@ part of the #error delivery agent.
Note that prior to V8.10, you had to use words or
codes here, not DSN values
(suchas 5.7.0), because the latter were wrongly broken up into five tokens. Beginning with
V8.10, you can also use DSN values here, and they will be handled properly. See ?§20.4.4
on page 720 for a full description of the #error delivery agent and for tables of useful words
and codes for the $@ part.
If the host is found and it is not an error delivery agent, that delivery agent is selected.
Otherwise, the unresolved host.domain is passed to other rule sets for further mailertable
lookups. Those other rule sets recursively strip the leftmost part of the host.domain away
and look up the result in the mailertable. This continues until either a match is found or
only a dot is left.
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