[9fans] mail rejection handling and spammers

[Sam <sah@softcardsystems.com>]

> back again and loops around 20 or so times before it finally gives up
> and returns it to the sender.
>

Something similar to this caused our cpu server to crash every so often,
befuddling us for a long time until we came in early enough to catch it
going down.  Turns out we were getting hammered by spammers who like to
send mail to a zillion usernames until one clicks.  The smtp processes
returning the mail accumulated until swap was gone and the cpu server fell
over.

We haven't upgraded to 4 yet, so I just hacked our code to drop those
messages (and likely more, based on my least-effort solution).

Anyone else experience this?

Cheers,

Sam