Why is my mail to HotMail (or AOL, Yahoo, etc.) subscribers not being delivered?

If the email doesn't make it through, and there's no bounce message returned, it's likely that it was filtered as spam.

Now I can hear you screaming already: "But it wasn't spam!!!"

I know, I know. That's the terribly frustrating part.

The problem is that email recipients are also screaming. They're screaming "How do I stop all this spam?" And ISPs and email providers such as HotMail, AOL and others, are scrambling to try and put into place solutions that halt, or at least seriously reduce the number of spam messages that get delivered to their customers.

The problem is that they sometimes go overboard, and mark legitimate email as spam.

Now, "marking" it as spam is annoying enough, but if that's all they did, that'd actual be less of a problem, since we'd still be able to look at it and decide what to do with it. Unfortunately, they've also taken to simply blocking and discarding much of what they see as spam.

And naturally, "what they see as spam" is a moving target. In attempts to improve the spam detection rate or react to the latest wave of actual spam, most folks are continually updating and upgrading the algorithms they use to tell spam from legitimate mail.

In the HotMail example I mentioned I pointed out that only mailing list subscribers that were getting the "digest" version of our mailing list were affected - folks getting the mailing list content in individual messages continued to receive them without problem. HotMail had decided that something about our digests looked like spam, and began discarding them. I assume they got complaints, because about a week later, they suddenly began to be delivered again.

For a while AOL used a technique called "rate limiting" - meaning that it would only accept so much mail in a certain amount of time from a particular sender. If you were trying to send more than that, you were likely a spammer, and the excess was discarded. What they failed to take into account were legitimate mailing list servers hosting multiple mailing lists that were attempting to send legitimate email across several mailing lists to a lot of AOL customers that had explicitly subscribed and requested it. After a while and many complaints, this technique also seems to have abated.

It sucks. Email providers are attempting to provide a valuable and legitimate service to their customers by blocking spam. And yet in their attempts to do so, they're often over-aggressively blocking legitimate mail, with no real recourse for legitimate senders.

So what can you do?

Well, I'll start by saying that there's no silver bullet. There's simply no way to guarantee that your email will be delivered, or guarantee that you'll find if it was or not. That's simply the nature of the world right now.

But there are things you can do to stack the deck in your favor.

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• Don't spam. I know, I know, you don't. Even so, don't do it. The key word is "unsolicited". Don't send people email that they didn't ask for, and don't put people on mailing lists without requiring double opt in. Anything less can get you legitimately branded as a spammer.

• Do everything you can to avoid looking like spam. My previous article Why is my mail to this person not getting through? includes a short list of many common things that can make your email start to look like spam.

• Check to see if your mail server has been blacklisted (not your PC, but the server that sends your mail - usually your ISP or your email service provider). Unfortunately this may, or may not, actually help you. There are so many different blacklists maintained by several entities, it's difficult to know which ones actually matter, and which ones might be responsible for your delivery problems. Even worse, getting off of blacklists can be extremely difficult, but at least it might give you some clues as to what might be happening. I have known people to change mail servers rather than deal with trying to get off of blacklists. ISIPP (Institute for Spam and Internet Public Policy) has How Can I Find Out If My Email Is Being Blocked? which includes links to serveral blacklist checking services.

• Check with the postmasters at the sites you're having trouble with. AOL has http://postmaster.aol.com/, Hotmail has http://postmaster.hotmail.com/, and most other large ISPs or EMail Service providers will have contact addresses that will at least claim to aid you in getting your legitimate email through. Quite often they'll have you jump through various hoops to do so - but remember, they're also counting on the fact that spammers are unable or unwilling to jump through those hoops.

• If it applies, consider using one of the accreditation services, or other email registries. While there's no general agreement yet on a single solution, publishing "SPF" records for your mailer, using "DomainKeys", or signing up for accreditation by a service such as SuretyMail can help get your legitimate email delivered, particularly if you are a large sender. If you use a third party email or mailing list service provider, you might investigate which of these techniques they employ.

• Educate your users. One of the most frustrating problems mailing list owners suffer from is subscribers using the "This is Spam" button to delete or unsubscribe from legitimate email that they actually requested (and often confirmed via a "double opt in" email). If they requested it, of course, it's not spam, and reporting it as such damages everyone.

As you can see, there aren't many concrete steps that can guarantee your email delivery. Without a bounce message telling you why, it becomes a guessing game. The best steps to take when you encounter a problem are to simply make sure that you're being a good email citizen, track down what clues you can, and possibly follow up with the ISP with which you're having delivery issues.