Email is still the most common way businesses communicate and the majority of people simply click send and assume their email is delivered, but when email messages bounce, there are a few things you should know.

Email Bounce

How Emails Work

The two most common protocols used to deliver your emails are Simple Mail Transfer Protocol (SMTP) and Extended SMTP (ESMTP). Each one has a set of codes it uses to identify what happens during the delivery, and you never see these.

Unless there’s a problem. Then you will see a string of information that tells you very little, unless you know the code. Since most organizations use a managed IT service to decipher and correct problems like these, they don’t need to learn every configuration and the descriptions, but it is helpful to know the general issues that are causing your emails to bounce.

Simple Fixes

First, you want to eliminate the obvious. A misplaced period, missing letter, or misspelling is the easiest to correct. Double-check that you have accurate information.

If you have the information right, the problem could be on the recipient’s end. Their mailbox could be full, or their server might not be locatable.

Perhaps the recipient is on vacation, in which case you could get an auto notification. This is not a bounce. It simply means they are not able to respond, but the email address is valid.

If the email address is listed as blocked, you may have to contact the person to have them either add you to their whitelist, which is their safe list, or get a different email address from them you can use to contact them.

Deciphering the Codes

When an email can’t be delivered you’ll see the SMTP codes. Those that begin with the number 4 indicate a temporary problem, and your server will keep trying to deliver. If you don’t see another bounce, the delivery was likely successful. If your server continues to try and still can’t get through, it will finally stop and let you know that it gave up.

If the code begins with a 5, this means it’s a permanent error, and your server will not try to deliver it again. A 550 tells you this is because the mailbox was unavailable, due to an incorrect email address or related issue.

A 552 error code will tell you the mailbox is full, or the message is too long or too big, based on the parameters set by the recipient’s mailbox.

The ESMTP codes use the three digits, but with periods between each digit. Those beginning with 4’s are still temporary, and 5’s are still permanent, but there are more details. For example, a 5.1.1 means the address part, left of the @, does not exist. If it’s the address section on the right of the @ that’s non-existent, then the code is 5.1.2. A code of 5.3.2 means the recipient’s email system won’t accept the message, possibly because it’s undergoing repair or maintenance.

After you review all the information, if you still find your emails are bouncing, it’s time to consult the experts. Your managed services IT company will be able to get the situation resolved and your connections restored.

ComputerHelpLA is the trusted choice when it comes to resolving email and other technical issues, staying ahead of the latest information technology with valuable tips, tricks, and news. Contact us at (310) 893-0878 or send us an email at for more information.


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