Since June 16th, the CERN SMTP gateway no longer accept email coming from hosts without a valid reverse DNS name for their IP address.

The Reverse DNS rule is now activated in the mail gateways. It means that a remote server (outside Cern) trying to send mails to Cern will be rejected if it has no reverse DNS entry configured in their DNS.
(Reverse DNS is used to get the server name from the IP address).

Users who get an error message:

550 5.7.1 Relaying denied. No reverse DNS configured for IP.

should contact their mail system administratorfor the remote servers, who must configure properly his reverse DNS.

Explanation: the change has introduced a better spam fighting by rejecting electronic mail from evident misconfigured mail servers that are typical used by spammer on hacked computers. The reverse DNS name is mandatory for a correct deliver of mail and it is now enforced. Properly configured remote mail
servers are unaffected by this change.

Wednesday 16 June 2004

Change is also explained in the MMM site, at URL:                                                                                               http://cern.ch/mmmservices/Help/?kbid=171011