[Exim] Retry Times for Bounce Messages

I've found that "ignore_bounce_errors_after" doesn't appear to work for
short time periods, e.g. "2h". I see frozen error messages that are 12
hours and older when this setting is set to "2h".

On a related note, as a potential wish list item. Would it be possible
to specify "retry rules" by sender (specifically the null sender '<>')?

I have problems with bounce messages that do not get hard errors on
delivery attempt accumulating on my mail queues. Ideally, I'd like to
specify retry rules and give up on sending any kind of bounce after a
certain time period.

Cheers,
Matt.