CheckMessageId = [true | false]
The CheckMessageId slow.conf configuration item allows the
Message-Id: header to be checked for validity.
If this CheckMessageId slow.conf configuration item is declared as
true (or if it is omitted which defaults to true), the Milter
Message-Id: header (if there is one in the
message) is checked for vality. If that header is missing or malformed, the
the mid event (as described in the
standard event set) is set.
A correctly formed
Message-Id: header must be surrounded
in angle braces, and must have a user-ish part to the left of an '@'
symbol, and a host-ish part to the right an '@' symbol.
It is malformed if any part is missing or if the host-ish part
lacks a dot.
If this CheckMessageId slow.conf configuration item is false, the above check is skipped.
If you do not control your MX servers, you may get
headers that were inserted my your MX servers. In that instance, it
will only be possible to check for missing
when messages are delivered directly to your own mail server.