Undeliverable error messages are the protocol in place to let you know when messages sent do not (for many reasons) make it to the intended recipient. You want to become familiar with how these messages relay exactly what the problem is. What causes you to get these messages?
- User gave incorrect email address – usually a typo.
- The user account no longer exists or their email box is at capacity (over quota).
- Spammer intentionally gave incorrect return address so that they will
not be identified and shut-down.
- If you use autoresponders, the auto could not be delivered due to any
of the reasons above and gets returned to you as undeliverable.
An “undeliverable” message will always give a reason explaining why the
message could not be delivered within the return message. A
typical return looks something like this:
The original message was received at Wed, 2, July 2011 18:45:05 -0500
(EST) from tiberius-t.isp.net [188.8.131.52]
—– The following addresses had permanent fatal errors —–
—– Transcript of session follows —–
… while talking to mx.rinku.or.xx.:
>>> RCPT To: [fake, wrong or erroneous email will be here]
<<< 550 … User unknown
550 … User unknown
These messages vary depending on the systems involved in the delivery of the email. Many times you will note that, if the spammer sent you junk mail through one of the addresses on your Web site that you have an autoresponder attached to, that the autoresponder couldn’t be delivered and your server is just letting you know this.
Remember, at the top of each returned undeliverable email is a code that gives you the reason the email could not be delivered. Here is a list of some of the most common error codes that you may run into when emails get returned to you:
- 421 Service not available, closing transmission channel
- 450 Requested mail action not taken: mailbox unavailable
- 451 Requested action aborted: local error in processing
- 452 Requested action not taken: insufficient system storage (mailbox full)
- 550 Requested action not taken: mailbox unavailable (mailbox not found, no access)
- 552 Requested mail action aborted: exceeded storage allocation (mailbox full)
- 553 Requested action not taken: mailbox name not allowed (mailbox syntax incorrect)
- 554 Transaction failed (timed out, resources, network issues)
Many undeliverable emails are due to a simple typo in the email address. And as spam increases, as discussed in earlier posts, returns due to “policy reasons” show your email was spammy and triggered spam filters.
Many times taking the time to look at the top of the returned email, lets you know exactly why the email bounced and what action, if any, you need to take.