Why you get so many "Returned mail: User unknown" emails

If you send an email to someone and accidentally mistyped their address, you will often get a message back that states your email couldn’t be delivered. But why do you get these “bounce back” messages regarding emails that you never sent in the first place? For the answer, read on ..

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 —–

< jdoe@email.com >
(reason: 550 5.1.1 < jdoe@email.com >… User unknown)

There are a number of reasons why these types of emails are coming into your Inbox and the most likely reasons are:

  • Someone has “spoofed” your email address, making it look like the email originally came from you. This is a popular tactic that spammers use to send their spam emails. 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 as though the email originated from you. In these cases, there isn’t much you can do to completely eliminate the problem because the spammer has simply guessed your email address and has inserted it into the From: field, making it look like these emails are coming from you. The best thing to do if you are receiving these types of emails is to flag the message as spam and move on.
  • Another possible reason for getting these emails is that 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 PC does not have a virus, another possible 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 will receive that message.
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