Exim verify recipient and MailScanner

[Paul Welsh]

Hi all

I'm running MailScanner 4.64.3 with Exim 4.6.  Apologies in advance if this
is deemed off-topic.

The problem is, I can't get Exim's verify recipient functionality working,
even though my exim.conf specifies it.

The reason I would like this to work is that my server relays for one domain
in particular that is getting thousands of dictionary based spam messages
(tens of thousands per day).  My server relays to their smtp server after
checking for spam and viruses using MailScanner and SpamAssassin.   The
public DNS for the domain points to my server as the MX and my server's DNS
has an MX of their SMTP server.  Their server sends their outbound mail via
mine so it gets scanned. 

The domain is in my /etc/virtual/relay_domains file and the IP of their mail
server is in my /etc/virtual/relay_hosts file.

Has anyone any ideas? I've spent hours banging my head against a brick wall
on this one.

What I expect to happen is for exim to contact the remote smtp server to
validate the address as soon as it gets the "rcpt to" command and then issue
an "unknown user" response.  What is happening instead is that the messages
are being accepted, scanned by MailScanner and passed to the remote smtp
server which rejects them.  This is a real waste of resources.

One theory I have is that because there's an inbound and outbound instance
of exim to allow it to work with MailScanner then the verify recipient
functionality is effectively disabled.

The /etc/exim.conf which is the instance of exim used for inbound mail has
these settings:

# accept if address is in a local domain as long as recipient can be
verified
accept domains = +local_domains
endpass
message = unknown user
verify = recipient

# accept if address is in a domain for which we relay as long as recipient 
# can be verified
accept domains = +relay_domains
endpass
message = unknown user
verify = recipient

accept hosts = +relay_hosts
endpass
message = unknown user
verify = recipient
accept hosts = +auth_relay_hosts
endpass
message = authentication required
verify = recipient