Returned mail: user unknown — Xfinity Email error message

What to do if you're getting returned mail messages that say "user unknown."

The subject of these bounced messages is often similar to

Returned Mail: User Unknown
Returned Mail: See Transcript for Details
Returned Mail: Delivery Problems Encountered
Mail Delivery Problem
Delivery Status Notification

The body of the message may be similar to the following

----- The following addresses had permanent fatal errors -----
< username@email!address.com > Reason: 550 5.1.1
< username@email!address.com >... User unknown

Why these types of email messages are coming into your inbox

• Someone has "spoofed" your email address, making it look like the email originally came from you. This is a popular tactic that spammers use. If any of the spam messages are sent to an address that doesn't exist, the email is bounced back to your account, since the spammer made it appear that the email originated from you. In these cases, all you can really do is use the Report As Spam feature in Xfinity Email or send these spam emails to missed-spam@comcast.net.

• A virus and/or worm may have infected your system. Make sure to update your anti-virus and firewall software and run a full system scan.

If you're certain that your computer does not have a virus, the more likely scenario is that an email virus and/or worm may have infected one or more of your friends' computers, and these people probably have your email address in their address book. The virus tries to spread itself by sending messages to many other users, using the address book of the infected computer. The virus/worm will often use a false address (yours) as the Reply-to: or From: address. If any of the messages that the virus sends bounce back, you'll receive that message.

Note: If the email address looks familiar, check the Sent mail folder. It could be possible that you misspelled the recipient's email address.