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.

Gabriel Torres is a Brazilian best-selling ICT expert, with 24 books published. He started his online career in 1996, when he launched Clube do Hardware, which is one of the oldest and largest websites about technology in Brazil. He created Hardware Secrets in 1999 to expand his knowledge outside his home country.