greylisting Inefficiency in deny_late mode

[Hans Salvisberg]

I run some of my domains with a catch-all address (i.e. no recipient 
checking), and I have a considerable number of retired addresses there. 
Many were never in actual use but have been invented by spammers! With 
this setup check_verybadrcptto takes care of about half of my spam, 
because a lot of spam includes one of the retired addresses in the 
recipient list.

greylisting takes care of much of the remaining spam, but I have to run 
it in deny_late mode, so that check_verybadrcptto can do its work (and 
issue a hard DENY). In deny_late mode, greylisting defers denials until 
hook_data (the documentation says hook_data_post, but this is wrong). 
However it still does its database work in hook_mail and/or hook_rcpt, 
even though a large number of transactions will receive a DENY before 
greylisting ever gets a hook_data call.

It would be nice if the greylisting database work could also be 
postponed until hook_data, when it's actually needed ("lazy 
evaluation"), so that it can be skipped, if some earlier plugin returns 
a DENY.

It would also be nice, if a plugin like check_verybadrcptto could 
somehow signal that the transaction is doomed, so that other, more 
expensive plugins could tell that they don't need to run anymore. I'm 
thinking of something like WILL_DENY and WILL_DENYSOFT that would set a 
status code that other plugins could test, and then they could decline 
immediately, unless they might return a more severe code.

Hans