It is very frustrating to send an email to someone and see the message bounce back. In this tutorial, we will explain the meaning of the most common bounce messages, show where the problem is located, and how to fix it.
For some reason, most users don’t read what is written in the bounce message; they call us and say “the message I sent you bounced back.” This simply doesn’t help, because without reading what is in the bounce message, it is impossible to understand what went wrong and how to fix the problem.
To make things worse, there is no standard for the way each bounce message is written, as each email server’s software uses different wording. In other words, the message that says, “this mailbox doesn’t exist” may be written in dozens of different ways, depending on the software running on the recipient’s email server.
However, each error message is accompanied by a three-digit error code, which is standardized – at least in theory. Unfortunately, some servers use the wrong code to describe the error. For example, the code 550 means “mailbox not available” (i.e., the email address doesn’t exist on that server), but some servers use, incorrectly, the code 554 for that.
Before we move on, one more piece of important information; it is very important to see if you really sent the message that generated the error message. There are viruses and spam software that send emails to random addresses, and sometimes the address they use in the “From” field might be your email address. If that happens, you will get a bounce message if the spam software or virus sent a message to an invalid email address, since your email was the one listed on the “From” field.
So, instead of seeing a legit error message, you might be facing an error message with spam or a virus attached to it. In cases like this, simply delete the error message, as it was not generated by a real email you sent.
There are three basic ways your email address may end up being used to send a virus or spam. The most common is by a random email address generator, meaning that the virus or spam software used your email address in the “From” field of the email, but the email was not sent from your computer or from your web-based email service – you just had the bad luck of having an email address identical to the email address the virus or spam software invented. In this case, there is nothing to worry about.
However, the spam or virus may be sent from your computer, if you have a virus installed on your computer that does that. Therefore, we recommend you run anti-virus program if you see a bounce message in your inbox containing spam or a virus.
The third way a virus or spam may be sent using your email is by someone hacking into your web-based email service, such as yahoo and gmail. If you use a web-based email service and see a bounce message with spam or a virus attached, we recommend you change your password.
Let’s now describe the most common errors, what they mean, where the problem is, and how to fix it.
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If you get error 550 (or 554, depending on the recipient’s email server), it means that the email address you are sending the message to does not exist.
Example of messages associated with this error:
550 [email] User unknown
550 Sorry, no mailbox here by that name. (#5.1.1)
550 Requested action not taken: mailbox unavailable
550 5.1.1 [email] is not a valid mailbox
550 No Such User Here
550 Invalid recipient
[email] (user not found)
5.1.0 – Unknown address error 550-‘MAILBOX NOT FOUND’
550-5.1.1 The email account that you tried to reach does not exist.
550 5.1.1 [e-mail]: Recipient address rejected: User unknown in relay recipient table
554 delivery error: This user doesn’t have a [name of the service] account
554 delivery error: Sorry your message to [email] cannot be delivered. This account has been disabled or discontinued
550 #5.1.0 Address rejected [email]
A message that is related to the same problem we are describing is this one, where the recipient’s host (i.e., email server) doesn’t exist:
Sorry, I couldn’t find any host named [host]. (#5.1.2)
If you got the email address from a real person, most likely there is a typo somewhere. Double check the email address you typed. If you obtained the address by phone, you may have misheard the name or a letter and ended up writing down the wrong email address.
However, if you obtained the recipient’s email from a website, from a magazine, an advertisement, etcetera, and you double-checked it to make sure there is no typo, this means that the email simply doesn’t exist. We know how frustrating this may be, but there is nothing we can do about it!
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If you get any of the messages listed below, this means the recipient’s mailbox is full and cannot receive any additional messages. The three-digit code associated with this error is usually 552. If this is the case, please let the person know by other means (telephone, Facebook or any other form of contact), so he or she can delete old messages and spam and solve the problem. This is a good example of why saying “the message I sent to you bounced back” doesn’t help the recipient, as he or she won’t know why; but saying “hey, your mailbox is full, you must delete some messages” will help him or her to solve the issue.
Mailbox is full
Disk quota exceeded
User is over the quota. You can try again later.
The recipient’s mailbox is full and can’t accept messages now.
Mailbox limit exceeded while appending message
Requested mail action aborted: exceeded storage allocation
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Let’s now talk about a few error messages you can see if there is something wrong with your email server configuration or if your email server is flagged as a source of spam. If you see any of the messages described below, you must contact the company that is hosting your email server (or the network administrator, in case you are using a corporate email address), so they can solve the issue.
451 Bad reverse DNS.
The “Bad reverse DNS” error message means that the email server you use doesn’t have a reverse DNS configuration, which is mandatory. You must contact the company that is hosting your email server and explain this so they can correctly configure the reverse DNS of the email server. The recipient’s email server is checking this configuration because virtually all servers without a reverse DNS configuration are servers built with the sole purpose of sending out spam.
blocked using b.barracudacentral.org;
Mail from [ip address] deferred using Trend Micro Email Reputation database. Please see https://www.mail-abuse.com/cgi-bin/lookup?[ip address]
553 User defined policy matched for [ip address]
These messages mean that the IP address of your email server is currently listed as a source of spam on a blacklist. You can follow the link usually provided by the error message to request the removal of the server’s IP address of the list and, after this request is completed by the maintainers of the blacklist, be able to send email to the recipient.
However, there is a good reason your email server’s IP address is blacklisted: someone is using it to send out spam. Therefore, you should report this error to the hosting company of your email server (or to the network administrator, in case you are using a corporate email address), so they can find who is sending out spam using the server, ban the culprit, and then request the proper removal from the blacklist. Otherwise, the IP address will be removed just to be added again, if the source of spam is not contained.
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Now we have some error messages related to bad configuration of the recipient’s email server. If you see a message similar to any of these, you must contact the recipient by other means (telephone, Facebook or any other form of contact) asking the recipient to contact the email server’s hosting company or the network administrator of the company (in the case of corporate emails) to fix the problem. Ideally, you should forward the error message to the recipient using a working email address, so he or she can forward to the person in charge of the email server’s configuration.
CNAME lookup failed temporarily. (#4.4.3)
Sorry, I wasn’t able to establish an SMTP connection. (#4.4.1)
If you get an error message that has something as:
THIS IS A WARNING MESSAGE ONLY YOU DO NOT NEED TO RESEND YOUR MESSAGE
This means that the recipient’s email server is facing a temporary issue, and your email server will keep trying to send the message (usually for the next four days). So, it is safe to simply ignore this error message. After this period (four days), if the message couldn’t be delivered, then your email server will generate a final error message, which you should analyze. Most likely, the problem will be at the recipient’s email server – as long as you didn’t mistype the recipient’s email address and the message ended up at the wrong server.
Of course, there are other error messages that you might see; we focused on the most common ones.
Understanding Email Bounce Messages
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