> The "standard" chkuser patch that vpopmail uses (see Bill
> Shupp's update to the original:
> http://www.shupp.org/patches/chkuser-0.6.mysql.patch) has
> some rather nasty behaviours.
> If for some reason your mysql server is unavailable (load has
> shot so high that mysql can't return a prompt reply, you're
> upgrading mysql, taking db down for maintenance, etc.) the
> chkusr patch will start telling remote smtp clients that the
> user doesn't exist. This is not good; you never want to send
> a 550 on a user that really does exist; people get upset when
> things bounce, and mailing lists start looking at auto-removal.
That explains a lot.
I thought the chkuser patch was awesome until I started seeing 550's
bouncing to customers for email addresses that aren't actually 550.
I'll be happy when the new patch comes about that fixes this issue.