I'd be very grateful if any of you could help with this maddening problem.
Our Exchange server in general recieves and sends mail with no problem.
However a few (and possibly increasing) number of domains are generating sender verify errors.
The Exchange server is 2003 Build 7638.2 SP2.
the domain is brantonbridge.co.uk with an mx record of mail.brantonbridge.co.uk.
Reverse DNS is set up and the IP matches the MX(A) record as far as i can tell.
The Anti - Spam we use is Pure Message 3.0.2.
A coupld of event log entries are listed here, and all email addresses listed are present and correct.
We do not appear to be on any blacklists - nor do we appear to be an open relay
SMTP Logging is set to maximum.
This is an SMTP protocol error log for virtual server ID 1, connection #109. The remote host "126.96.36.199", responded to the SMTP command "rcpt" with "550-Verification failed for <email@example.com> 550-The mail server could not deliver mail to firstname.lastname@example.org. The account or domain may not exist, they may be blacklisted, or missing the proper dns entries. 550 Sender verify failed ". The full command sent was "RCPT TO:<email@example.com>
This is an SMTP protocol error log for virtual server ID 1, connection #16. The remote host "188.8.131.52", responded to the SMTP command "mail" with "550 Unable to verify sender ". The full command sent was "MAIL FROM:<firstname.lastname@example.org> SIZE=9118 ". This will probably cause the connection to fail.
Many thanks in advance.