One of the benefits of ExchangeDefender is that we allow our clients to process both their inbound and outbound mail through ExchangeDefender and eliminate SPAM in both directions. Until now we allowed IP based relay on our outbound network even if the domain name was not protected by ExchangeDefender. While this was a matter of convenience, the explosion of compromised servers and virus distribution is starting to create an “open relay” problem for ExchangeDefender: where third party domains are relaying through our clients servers and forging the From: address.
Effective March 22nd, ExchangeDefender will only permit outbound relay from email domains that are protected by ExchangeDefender and have their MX records pointed to ExchangeDefender nodes. Any attempt to send email through the ExchangeDefender by a 3rd party domain not protected by ExchangeDefender will be rejected.
If you have a business case scenario that requires you to relay third party domains that are not protected by ExchangeDefender (because you don’t own the domain name, do not have administrative control, shared domain with another organization) we recommend that you relay those messages directly via your SMTP service / IP address instead of attempting to route them through the ExchangeDefender smarthost.
Note: This policy change will not affect any legitimate traffic going through our outbound network. It only picks up illegal spoofed traffic based on the From: line (if it includes a domain name not protected by ExchangeDefender)