Beginners start here: When e-mail goes bad

Sean McNamara
19 June, 2008
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E-mail has become such a staple of our online lives that it’s hard to imagine how we got by without it. However, it’s not a perfect system, and there are many things which can go wrong at all stages of delivery. Here’s a look at some of the most common causes of e-mail delivery problems and what can and can’t be done about them.

One of the most confusing aspects of e-mail is error reporting when something goes wrong with delivery. There are, in fact, standard lists of error codes and types, but each e-mail server program seems to have slightly different wording for the same types of errors, and it is possible with some mail server programs to change the description of any or all of the error codes. It would be nice to have your e-mail client interpret the error message for you, open the original message and highlight where the problem might be, but we’re a long way from such a useful system.

Most people I know throw their hands up when they receive an error report and just think it’s a problem with the receiving server or computer. They don’t try and decipher the report, and therefore may miss problems with their own configuration or data, their server or ISP’s settings, or useful information on how to get around the problem.

Here’s a sample of some of the error description lines from the last seven years of my e-mail:

  • The user(s) account is temporarily over quota.
  • User mailbox exceeds allowed size:
  • The recipient name is not recognized
  • Reason: Recipient Rejected: Account Inactive
  • Reason: 5.3.0 <>… No such user
  • Reason: 5.1.1 <>… User unknown
  • Reason: This account is not allowed…
  • DNS for host is mis-configured
  • The queue containing messages destined for was expired by the Postmaster of
  • Host not found
  • Message undeliverable. Your email address is not listed in the Address Book of — [101]
  • The e-mail system was unable to deliver the message, but did not report a specific reason. Check the address and try again. If it still fails, contact your system administrator.

As you can see, some of them are very similar to each other and some are more helpful than others (with the last one being pretty well useless). However, these lines are often buried amongst lines and lines of gobbledegook, and can be hard to extract to do anything with.

It is worth trying to find these error descriptions, as they may help to resolve the problem. For example, the "over quota" and "exceeds allowed size" would tell you that the recipient needs to clear out their inbox — this is most likely a transient problem and trying again later will probably work (especially if you inform the recipient via other means, such as the phone).

A related error is if your sending mail server is happy to receive a large e-mail, but the receiving server is not. For example, most receiving mail servers won’t accept an e-mail over 10MB (and with the overhead for encoding for attachments, that means you’re limited to a 6-7MB attachment), but some sending mail servers will accept messages larger than 10MB — so the message initially seems to be accepted, only to get bounced back at the other end. Try again with a smaller attachment or, if there’s more than one attachment, send them separately.

The "no such user"-type messages mean that the recipient’s e-mail address is either no longer valid or it’s been entered incorrectly. In these situations, it’s worth trying again by typing in the whole address manually (rather than relying on what might be an incorrect address book entry) or verifying the address with common correspondents or the intended recipient. The most common cause of this sort of error when the address is actually valid is the inadvertent entry of disallowed characters in the address such as commas, spaces, slashes, etc.

Although delivery error messages have a long way to go before becoming universally useful, they can help get past problems you might be experiencing with getting mail delivered. They’re worth at least a quick look in case the fix is easily determinable.

Next time, I’ll look at the most common configuration problems which can cause your e-mail program to misbehave.

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