[COLUG] Exim4 Recipient Whitelisting

[Dave Maxwell]

I have an Exim4 instance in front of an Exchange 2000 server acting as a 
ClamAV/SpamAssassin filter.  Exchange 2000 does a very very braindead thing 
with non-existent users.  It will quietly accept the mail then mail a bounce 
to the From: an hour or two later. This makes deliberate use of blowback for 
spam bouncing trivially easy. Doing a callout/verify on the Exim4 side 
doesn't work as Exchange will vouch for any To: that has 
@exchange_servers_domain.com.  Exchange 2000 simply doesn't have the ability 
terminate at SMTP receive time mails to non-existant recipients. 

What I need to do is simply give Exim4 a list of valid recipients.  I could 
then reject mails to non-existent recipients at SMTP connection time.  It is 
a small business with low turnover and having small text file on the Exim4 
side of valid recipients is an entirely practical means to deal with this.

I've found many many howtos on Sender verification and almost everything I've 
found on recipient verification assumes a callout to the smarthost works 
correctly.

The only other way I've found to do it is to make Exim4 query Active Directory 
over LDAP to test recipient validity.  If I have no choice, I'll do it that 
way but I'd prefer something less 'brittle'.

Thanks

Dave

-- 
Oh yeah.  Forgot about those.  Getting senile, I guess...
		-- Larry Wall in <199710261551.HAA17791 at wall.org>