Why Can’t My Mail Server Deliver Mail to Yahoo! or AOL?

With constantly growing spam volumes, large email providers have been forced to take measures to reduce spam’s impact on their infrastructure and on their customers. Unprotected email systems are easily crippled by spam outbreaks and it doesn’t make sense to overbuild capacity to meet what-if situations.

One way large email providers protect their systems is through the use of a reputation database along with mail architectures which use the database to rate-limit or block emails. AOL, Yahoo!, and others maintain proprietary reputation systems. The following best practices can help maintain your good reputation – improving your mail deliverability not just to Yahoo! and AOL but to everywhere.

If you are having problems with your emails bouncing or being treated as junk, there are three steps you can take which can improve your deliverability:

A) Check the reverse DNS entry for your outbound mail server’s IP address

1. Make sure the forward and reverse match.If your IP resolves to example.com, make sure that one of the addresses that example.com resolves to is your IP.
2. Make sure its set for your server specifically, preferably tothe domain you are sending mail from.
3. Don’t use an address that looks dynamic. A reverse DNS of d192-168-0-1.example.com is considered a much likelier source of spam then “mail.example.com”.

B) Avoid having your server look like a source of spam

1. Old email accounts are often forwarded to a new address. If the address your server forwards to is eventually de-activated, does your email server stop forwarding messages to it? Many won’t automatically. This will mean your server is regularly sending email to an invalid recipient – something that spammers do.
2. If possible, forward email after spam filtering. This can help reduce the impression that it’s your server that originated the spam. It may also help keep your mail queue from filling up with messages which aren’t accepted by the server you are forwarding to.
3. Ensure good list hygiene practices. Whether its someone in marketing sending email from their desktop or a properly managed list using list management software, your responsibilities are the same. Only email people who actually want to hear what it is you are saying to them. Promptly handle and always respect any requests to unsubscribe. Unsubscribe addresses which bounce repeatedly. Comply with CAN-SPAM.

As an email server administrator, configuring your server correctly can go a long way to following these guidelines, but that is only one piece of the puzzle. Your users needs to be educated, and your mail server’s logs need to be reviewed periodically. Your pro-active approach will help avoid having your user’s productivity impacted when they can’t email their contacts.