Horses, not zebras


I was first introduced to the maxim “When you hear hoofbeats, think horses not zebras” when I worked in my first molecular biology lab 20-some-odd years ago. I’m no longer a gene jockey, but I still find myself applying this to troubleshooting delivery problems for clients.
It’s not that I think all delivery problems are caused by “horses”, or that “zebras” never cause problems for email delivery. It’s more that there are some very common causes of delivery problems and it’s a more effective use of time to address those common problems before getting into the less common cases.
This was actually something that one of the mailbox provider reps said at M3AAWG in SF last month. They have no problem with personal escalations when there’s something unusual going on. But, the majority of issues can be handled through the standard channels.
What are the horses I look for with delivery problems.

  1. Technical issues. These are actually getting rarer as companies move to the designed-for-bulk MTAs like MessageSystems and Port25. But they’re still worth checking and can contribute to delivery problems. Luckily, technical issues are often the easiest to solve, and once they’re solved usually stay solved.
  2. Content issues. These are getting much more common as ISPs start looking at all the URLs and links in emails, including the landing pages.  Gmail, for instance, does almost all their filtering based on content rather than originating IP. This is not that difficult to solve, but can be harder to solve than technical issues.
  3. Address collection issues. Most delivery problems start at the point of address collection, and these can be challenging problems to solve. Not only do you have to solve the problem moving forward, you also have to decide what to do with the addresses you’ve previously collected. And the problems are only solved as long as someone knows why things are done the way they are.


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