Email Deliverability Tips: 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.

Post #1 on Why Spam Filters Suck "trickle blog" series

A Short History of Spam Protection

While methods have changed, spam continues to be the misuse of an open communication network for financial gain. What was once a harmless annoyance has led to serious conditions where high spam traffic can clog email servers to the detriment of legitimate mail.

How did we get here? And what can we change to solve the problem?

The first spam email ever was used to promote a seminar from Digital Equipment Corporation (DEC) in 1978. I'd call it spam because it was a mass emailing harvested from a printed directory of ARPAnet to recipients who had not requested any contact.

Spam didn't become a huge problem until around 2002 when there were enough active email users worldwide to make spamming profitable. In response, the first commercial and open source spam filters arrived in Brightmail, PureMessage, and SpamAssassin to name a few. The first generation of filters applied sets of rules to each message received, identifying features within messages which might indicate the likelihood
of being spam.

Spammers countered rule-based filters by obfuscating the content of their messages. Rather than sending a text message advertising Viagra, for example, the spammer might chop the message into small HTML pieces which, while unrecognizable to the spam filter, would still render into legible text for the message recipient. The rule-based filters added more rules to catch these obfuscations, causing the spammers to further innovate. This pattern of content obfuscation continues to the present day, the most recent example of which is probably MP3 spam (i.e. spam message contained in an audio file).

Anti-spam is one of those areas of IT where you're "damned if you don't." If email is flowing free of spam, you hear nothing. But when spam is getting through or emails are backlogged on the server, there's hell to pay.

Why is spam causing backlogs? Why is all mail treated equally? And do we need to keep adding what are effectively junk processing servers?

As the sophistication of spam has increased so has the need for processing power to analyze those messages. Today, with email servers under high traffic loads, the ever increasing computational cost and processing overhead of analyzing the content of every email often results in service disruptions for legitimate email. This has to change. IT infrastructure costs should be a function of legitimate activity not spammer driven loads.

To solve the loading problem imposed by the current method of spam filtering where all incoming email messages are accepted by the server, buffered in a common queue on a first-come first-served basis, there needs to be a shift away from a single-queue of email traffic towards a prioritized system that can expedite legitimate mail first.

But there's more that needs to be considered...

UPDATE: On the subject of the history of spam, Christopher Nickson writes that the word "spam" to describe unsolicited commercial email recently celebrated it's 15th anniversary.

NEXT: Post #2 Prohibition Induces "Botlegging"

Santa Likely To Receive Over A Billion Spam Emails This Christmas!

You may not believe in Santa Claus, but surely you must believe in Wikipedia, and that's enough to read this post.

According to Wikipedia roughly 33% of the World's population are Christians, the World's population is currently around 6.6 billion, and the average life expectancy is 67 years. Let's assume that 80% of children believe in Santa Claus and on average stop writing to Santa Claus at around 12 years old. Now let's assume that 50% send an email to Santa requesting a new train-set or pony.

The number of emails Santa Claus will receive this year is (6.6 billion * 0.33 * 12/67 * 0.80 * 0.50) approximately 150 million emails from excited children. That's a lot of emails! Now let's assume that poor old Santa Claus has been too busy reading emails to install an email security solution. Since his email address is so well known (santa AT thenorthpole DOT com) and the spammers, who believe in him, know he reads all his email, he'll likely be receiving over a 90% spam rate.

If only 10% are legitimate email, he'll be looking at 1.5 billion emails, 1.35 billion of which are spam!

So as you're getting ready for Christmas, or whichever holiday you celebrate, spare a thought for Santa Claus.