Understanding Undeliverable and Returned E-mails

I get asked about this all the time from my clients, so I thought I would share with you today information on how to decipher undeliverable and returned e-mails.

The several common reasons you may receive undeliverable e-mail returns:

You had a typo in the e-mail address making it incorrect and therefore undeliverable. Conducive to dialing an wrong phone number.
The person you are e-mailing actually gave you an incorrect e-mail address (typo) – that happens allot!! That’s why it is a good idea to have your Web site contact forms have visitors enter their address twice.
The recipient’s inbox is filled to capacity due to large attachments or not logging in for a while. What many times causes this problem is the user has “leave mail on server” checked in their e-mail program which then does not allow their e-mail account to be cleared. All e-mail is “left on the server”. Until that option is unchecked and all e-mail is downloaded to clear out their e-mail account this will continue to happen. Leave this option unchecked unless you can micro-manage it!
Your autoresponder message could not “auto respond” to a bogus e-mail address that a spammer used to e-mail you.
Your e-mail was “spammy” and set off spam or network security filters.
Someone who has your e-mail address on their system has a virus that is propagating itself to old or no longer live e-mail addresses putting your address in the FROM: field. This causes undeliverable virus generated e-mails to be return to you.

Undeliverable error messages are the protocol in place to let you know when messages do not (for many different reasons) make it to the intended recipient. You want to become familiar with how these messages display exactly what the problem is.

With all returned e-mails, there will always be an “undeliverable reason” at the top of the e-mail as to why the message could not be delivered. Many of you have noticed as of late the rash of Undeliverable Messages being returned by your ISPs due to viruses.

If you look closely at the returned message you will see what the problem was – they look similar to this:

The original message was received at Thu, 21 Aug 2008 12:38:48 -0700 (PDT)
from adsl-157-24-41.irving.bellsouth.net [60.127.21.47]

—– The following addresses had permanent fatal errors —–

(reason: 550 5.1.1 … User unknown)

—– Transcript of session follows —–
… while talking to theistudio.com.:
>>> DATA
<<< 550 5.1.1 … User unknown
550 5.1.1 … User unknown
<<< 503 5.0.0 Need RCPT (recipient)

The above reflects that there is no such e-mail address on that system (theistudio.com) – user unknown. You will always see the actual e-mail that could not be delivered below the error message so you can see if it is in fact an e-mail you sent, your autoresponder or a virus generated e-mail that you did not send.

Here is a listing of the most common error codes you will see in undeliverable e-mails and what they mean:

251 User not local; will forward to 421 Service not available, closing transmission channel
450 Requested mail action not taken: mailbox unavailable (E.g., mailbox busy)
451 Requested action aborted: local error in processing
452 Requested action not taken: insufficient system storage
500 Syntax error, command unrecognized
501 Syntax error in parameters or arguments
502 Command not implemented
503 Bad sequence of commands
504 Command parameter not implemented
550 Requested action not taken: mailbox unavailable (E.g., mailbox not found, no access)
551 User not local
552 Requested mail action aborted: exceeded storage allocation (mailbox filled)
553 Requested action not taken: mailbox name not allowed (E.g., mailbox syntax incorrect)
554 Transaction failed ( Example: 554 5.7.1 Forbidden for policy reasons — Your e-mail was identified as spammy.)

These messages will vary depending on the systems involved in the delivery of the e-mail. It is worth becoming familiar with the basics so that you don’t panic or assume there is a problem where there may not be one.

HTH!