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Understanding Undeliverable and Returned Emails

Do you get undeliverable email returns or bounce-backs and are unsure what they would mean. You are not alone! I get asked about this quite often so I thought I would share with you information on how to decipher undeliverable and returned emails.

The several common reasons you may receive undeliverable email returns:

  1. You had a typo in the email address making it incorrect and therefore undeliverable. Conducive to dialing an wrong phone number.
  2. The person you are emailing actually gave you an incorrect email address (typo) – that happens a lot! ? That’s why it is not such a bad idea to have your website contact forms have visitors enter their address twice.
  3. The recipient’s inbox is filled to capacity due to large attachments, server settings or not logging in for a while. What many times causes this problem is the user has “leave mail on server” checked in their email program which then does not allow their email account to be cleared. All email is “left on the server”. Until that option is unchecked and all email is downloaded to clear out their email account this will continue to happen. (Leave this option unchecked unless you can micro-manage it!)
  4. Your autoresponder message could not “auto respond” to a bogus email address that a spammer used to email you.
  5. Your email was “spammy” and set off spam or network security filters.
  6. Someone who has your email address on their system has a virus that is propagating itself to old or no longer live email addresses putting your address in the FROM: field. This causes undeliverable virus generated emails 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 emails, there will always be an “undeliverable reason” at the top of the email as to why the message could not be delivered. 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 Wed, 08 Nov 2017 10:38:48 -0700 (PDT)
from adsl-157-24-41.XXXXX.XXXXXX.net [12.345.67.89 ]

—– The following addresses had permanent fatal errors —–

(reason: 550 5.1.1 … User unknown)

—– Transcript of session follows —–
… while talking to businessemailetiquette.com.:
550 5.1.1 … User unknown

The above reflects that there is no such email address on that system (businessemailetiquette.com) – 550 user unknown.

The actual email that could not be delivered will be displayed below the error message so you can see if it is in fact an email you sent, your autoresponder or a virus generated email that you did not send.

Here is a listing of the most common error codes you will see in undeliverable emails 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 email was identified as spammy.)

These messages will vary depending on the systems involved in the delivery of the email. It is worth becoming familiar with these basics (or bookmarking this page) so that you don’t panic or assume there is a problem where there may not be one.

Go ahead and share!