Many MTAs support access databases, such as Sendmail, Postfix, etc.
This plugin does similar checks to see whether a message would have
The rule returns false if an entry isnt found, or the entry has a RHS of
OK or SKIP.
The rule returns true if an entry exists and has a RHS of REJECT, ERROR,
Note: only the first word (split on non-word characters) of the RHS
is checked, so error:5.7.1:... means ERROR.