Ever have an email “bounce-back” and wonder why? There is a specific protocol in place to let you know when messages do not (for many reasons) make it to the intended recipient. Being familiar with how this process works can help you to determine what the issue is and why the email was returned to you.
What causes these messages?
Here are a few of the reasons:
- The user gave an incorrect email address – usually a typo.
- The user account no longer exists (or is experiencing technical difficulties).
- The email box is at capacity (over quota).
- A spammer intentionally gave an incorrect return address.
- Automated messages (autoresponders) are susceptible to the above reasons as well.
An undeliverable or bounce-back message will always give a reason explaining why the message could not be delivered within the return message. The return message you receive will also include an undeliverable error code. A typical return looks something like this:
The original message was received at Thur, 18, March 2021 18:45:05 -0500
(EST) from domain.isp.net [207.69.XXX.XXX]
—– The following addresses had permanent fatal errors —–
—– Transcript of session follows —–
… while talking to mx.domain.or.xx.:
>>> RCPT To: [fake, wrong or erroneous email will be here]
<<< 550 … User unknown
550 … User unknown
Messages Will Vary
These messages vary depending on the systems involved in the delivery of the email. For example, if you have automated responses engaged. When a spammer sends you an email, your autoresponder most likely will bounce back due to the spammer’s bogus address.
At the top of each undeliverable email is a code that will detail for you the specific reason the network was unable to deliver your email. Here is a list of some of the most common error codes that you may run into when you find bounce backs in our inbox.
- 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. Second to that comes spam. And if your email is spammy it may trigger spam filters that can cause the server on the other end to reject that email.
In most cases when you take the time to look at the top of the returned email, you will find exactly why the email bounced. Then you know what action if any, you need to take.