You check your e-mail and there is an “undeliverable email” in your inbox — what the heck is going on? Well, let’s figure that out, shall we?

There can be a bunch of reasons why e-mails cannot be delivered.

Common reasons you may receive undeliverable email returns:

• You had a typo in the e-mail address making it incorrect and therefore undeliverable. Conducive to dialing a wrong phone number.
• The person you are e-mailing actually gave you an incorrect e-mail address (typo) – that happens a lot!
• Their inbox is filled to capacity due to large attachments or not logging in for a while. Another cause is they have “leave mail on server” checked in their e-mail program which then does not allow their e-mail account to be cleared as 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 micromanage it!
• A spammer used a phony e-mail address when sending to you and your autoresponder message could not respond to the bogus e-mail address.
• Someone who has your e-mail address on their system has a virus that is propagating itself to old or non-existent e-mail addresses putting your address in the FROM: field. This causes undeliverable virus generated e-mails to be returned to you.

It’s All in the Bounce-back Email

Undeliverable e-mail messages are also known as bounce-backs. There is a protocol in place to let you know when messages you send do not (for many different reasons) make it to the intended recipient. Becoming familiar with how these messages are structured can help you determine exactly what the problem is.

With all returned e-mails, there will always be an “undeliverable reason” at the top of the e-mail. This will tell you why the message could not be delivered. If you look closely at the returned message you will see what the problem was. The top of the message will look similar to this:

Example Returned E-mail Header

This message was created automatically by mail delivery software.
A message that you sent could not be delivered to one or more of its recipients. This is a permanent error.
The original message was received at Wed, 2 Aug 2017 18:45:05 -0500 (EST) from providers.isp.net [207.XX.XX.XX] —– The following addresses had permanent fatal errors [email protected] while talking to mx.servername.com.: >>> RCPT To: <<< 550 … User unknown

The above example reflects that there is no such e-mail address on that system – user unknown. The provider’s domain, IP and other side’s mx server information will be replaced with the actual data for the e-mail that was returned as undeliverable to you.

These messages vary depending on the systems and software involved in the delivery of the e-mail. In some e-mail programs you may have to click View > Message Source to see all the background routing info and server error code. Some will be simpler:

[email protected], ERROR_CODE :554, ERROR_CODE :5.7.1 Message blocked due to spam content in the message.

The above lets you know that 554 (transaction failed) and why. You were identified as spam or doing something spammy. Of course my readers don’t spam, so you would then need to contact the recipient and get them to add you to their whitelist/approved senders/address book.

There will be minimally the header (Date, From, To and Subject:) of the e-mail that could not be delivered below the error message. This will help you determine if in fact it was an e-mail you sent, your autoresponder or a virus generated e-mail that you did not send.

Listing of the Most Common Error Undeliverable E-mail Codes:

• 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

Bookmark This Page!

Now you can look at a returned e-mail and understand what happened! You’ll also be able to determine if what happened is in your control to control. For example your typo versus mailbox filled scenario. Go ahead and bookmark this page right now so you can refer to it as needed.