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 #2 on Why Spam Filters Suck "trickle blog" series

Prohibition Induces "Botlegging"

Spamming is a "tragedy of the commons," in which a finite resource (our time and attention) is abused at low cost by a minority (the spammers). Like many such tragedies in our human history, prohibition has been seen as the quick fix. Classic targets of prohibitionism include alcohol, drugs, and gambling. The idea is simple really. Stop spammers from profiting by making the actions illegal, enforceable and a harmful choice to the culprit. However, this kind of law is difficult to enforce.

In 2003, American legislators passed the CAN-SPAM Act (Controlling the Assault of Non-Solicited Pornography And Marketing). CAN-SPAM made it illegal to send unsolicited bulk email with a deceiving subject line and forced legitimate senders to identity themselves with a full mailing address.

So why then, does spam volume continue to rise despite an increased adoption of spam blocking mechanisms worldwide?

Several years have passed and spam volume is higher than ever. While CAN-SPAM is rightly criticized for not ending the spam problem, its most significant side effect was to force spamming underground and out of the reach of law enforcement. Face with service interruptions, spammers began in early 2004 to migrate their operations to a highly scalable distribution platform immune to law enforcement: the botnet.

By the end of the same year, the majority of spam was being delivered by decentralized networks such as "Phatbot" - and nowadays by Storm, Mega-D, and Srizbi - lending little hope to Bill Gates' famous pronouncement that spam would be beaten before the end of 2006.

The fact is that there are limitations with each anti-spam technique. Content filters are a core component of that architecture and are very effective at separate spam from email once they receive and recognize it. DNSBLs can block bad senders from known IP addresses once they known the sender is bad. But what happens when a botnet harvests new zombies with IP addresses unknown to DNSBLs and uses those to send new spam campaigns – something that happens every day? Discarding spam after you receive it does nothing to decrease high spam traffic from new campaigns. What is needed is a combination of the best-of-breed elements suited to deal with each type of spam: known content, unknown content, known senders and most importantly the unknown sender.

If you're doubling servers to deal with heavy spam loads, your infrastructure costs are under control of the spammers who can just keep sending more spam. What you need is a new solution that can block most spam without having to receive the message first in order to get the costs and the load back under control and ensure your infrastructure is used to deliver legitimate mail first.

NEXT: Post #3 Once Promising Proposals for a Final Ultimate Solution to the Spam Problem (FUSSP)
PREVIOUS: Post #1 Short History on Spam Protection