Bug 7436

It would be nice to be able to add expiry dates to rules so SpamAssassin automatically ignores them after the expiry date.

The use case is locally-created rules designed to deal with a specific spam run that don't have long-term value; the expiry date both expires them out after a while and documents the fact that they're temporary.

This feature is intended for site rules, not centrally-distributed ones because giving spammers knowledge of expiry dates is not a good idea.

Issues to consider:

1) Meta-rules: What if a component rule expires?  Possible ways to deal with this are to ignore expiries on rules that are part of a meta rule, or alternatively ensure that the meta-rule expires at least as soon as the component rule.

2) How to expire rules?  If a rule is already expired when the config file is read, it can be discarded.  But in a daemon that might not read the config file often, we'd need a place in memory to store the expiry date of a rule and delete it once that date has passed.

3) How to express in the config file?  Ideas so far are one of:

   expire RULENAME yyyy-mm-dd

or

   tflags RULENAME expire=yyyy-mm-dd

4) (Ambitious) What about a utility script to parse the rules file and clean out old rules?  That is, copy an input rules file to an output rules file, omitting expired rules.