Understanding Undeliverable Emails

You check your email and find an “undeliverable email” in your inbox. We also refer to these as bounce backs. These are also known as bounce-backs. What the heck is going on? Well, let’s figure that out, shall we?

There are several reasons why emails may not reach their intended destination. Consequently, some are beyond your control.

Common reasons you may receive undeliverable email returns:

You had a typo in the email address, making it incorrect and undeliverable. Conducive to dialing the wrong phone number.
The person you are emailing gave you an incorrect email address (typo).
The recipient’s inbox is at capacity due to large attachments or not clearing their inbox. (Email settings can be the cause of this.*)
Use an autoresponder or away message? A spammer used a phony email address, and your autoresponder message could not respond to the spammer’s bogus email address.
Get a bounce showing your email address, but you didn’t send it? Someone may have your email address on their system, and a virus is propagating itself, inserting your address in the ‘From:’ field to old or non-existent email addresses. Or just spammers being sneaky.

*AVOIDING FILLED INBOXES:

The primary cause of an inbox hitting capacity is the “leave mail on server” setting in your email program. This setting does not allow that email account to be cleared because the email is “left on the server.”

Over time, emails accumulate. And contrary to assumptions, email providers do not offer unlimited storage; at some point, additional charges may apply.

This will continue until the option is unchecked and all emails have been downloaded, clearing the email account. Leave this option unchecked unless you can micromanage it.

Another thing to be aware of is that you do not want to have all your devices set to “Leave mail on server.” If you do, you’ll never empty your inbox and could face emails bouncing due to capacity issues.

For example, you can set your cellphone to “Leave mail on server” so when you do email on your phone, you are just “viewing” your email and everything you do is synced with the server. You then download all your emails (Leave mail on server unchecked) from your PC or laptop.

Some also view their email service as a service to store and file emails for perpetuity. Don’t make that mistake. Review your provider’s capacity limits and explore potential data storage options.

It’s All in the Bounce-back Email

Undeliverable email messages are also known as bounce-backs. Did you know that a protocol is in place for this process? This protocol lets you know when messages you send do not reach the intended recipient and why.

When you become familiar with how these messages are structured, you can determine the exact problem. Similarly, becoming familiar with the various reasons will help you understand what is happening.

There will always be an “undeliverable reason” at the top of the email with all returned emails. This error code will tell you why the message was not delivered.

Example Returned Email Header

Email headers are not shown automatically. Here’s how to view them in Outlook. Upon examining the returned message closely, you will see the problem. The top of the message will look similar to this:

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, 19 June 2024 18:45:05 -0500 (EST) from providers.isp.net [207.XX.XX.XX] —– The following addresses had permanent fatal errors bl******@****in.com while talking to mx.servername.com.: >>> RCPT To: <<< 550 … User unknown

The above example reflects that no such email address exists on that system. The User is unknown. We have an email address that is incorrect or inactive.

Using the example above, you can see the actual provider’s domain, IP, and MX server (mail server) information reflect the exact data for that particular email, as evidenced by the 550 error code.

These messages vary depending on the systems and software used to deliver the email. For example, in some email programs, you may have to click View > Message Source to see all the background routing information and server error codes.

Then, some systems are simpler:

bl******@****in.com, ERROR_CODE :554, ERROR_CODE :5.7.1 Message blocked due to spam content in the message.

The above indicates that 554 (transaction failed) and provides the reason. You were identified as spam or engaging in spam-like activity. Of course, my readers don’t spam, right?

Moving forward, get in the habit of asking those you email to add your email address to their whitelist/approved senders list/address book. If you have a website, ask subscribers and visitors to do the same to ensure they receive your response.

In bounce-backs, below the error message, there will be at least the header (Date, From, To, and Subject:) of the email that could not be delivered. This will help you determine if it was an email you actually sent. Or if it was your autoresponder, bot, or virus-generated email, you did not send.

Listing of the Most Common Error Undeliverable Email 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

Some of the codes above are technical and have more to do with the “system” than anything you can address. If you are unsure when you receive a bounce-back, send a copy of the return message to your email provider.