MailScanner as mail proxy

[David Lee]

On Tue, 31 Oct 2006, Marc Lucke wrote:

> I know this is getting off topic.  I know enough about sendmail to be
> 99% sure that this question should be on their list.  But any help,
> ideas or feedback would be welcome.  I'm guessing the MailScanner
> community would have come across my problem on more than 1 occasion.
>
> I run MailScanner on a remote machine to my actual mailserver.  In other
> words all mail is relayed via the Mailscanner box.  This is to stop
> viruses and spam on the mailserver I have to run which is very limited
> in such defenses.  It all works great, apart from one annoying problem:
> if someone sends to an unknown email account (as oft occurs) the
> MailScanner proxy (for want of a better way to describe it as I'm using
> it) first accepts the email, attempts delivery, cannot deliver and then
> tries to notify the sender who doesn't exist.  So I'm lumbered with a
> billion postmaster non-delivery emails.  I'm keeping up with this quite
> well, but I'm scared I'll miss a legitimate message because it's buried
> in garbage.
>
> Is there anything I can do to get anything in MailScanner to check with
> my destination email server that the actual account exists before
> accepting the email in the first place?

Even MailScanner would be too late: your overall email system has already
accepted the email.  To confirm your last paragraph, for unknown
usernames, you really need to refuse to accept the email in the first
place.

You need to do your "refuse to accept" on your Internet boundary: on the
sendmail listener that runs on your remote (MailScanner) box.  A route you
probably want to investigate is the "virtuser" table in that remote
sendmail listener, and having a maintenance procedure that regularly
populates that table with the valid usernames (and other possible valid
addresses) on your user-mailserver.

Then (as you say) take any further questions to the sendmail list.

Hope that helps.



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