Getting bounce back e-mails from addresses I don't know
Bounced e-mails are e-mails that do not reach their destination, because of an error in transmission, or because they were addressed incorrectly (user error). When an e-mail bounces, it is returned to sender.
There are many reasons why e-mails should bounce. However, bounced e-mails may also be the result of a malicious e-mail, or unwanted e-mail (spam).
Why spammers and cons may do this
1. A spammer may circulate through millions of e-mails addresses, using each as the sender to help deceive the spam filter into thinking the messages are coming from multiple sources.
2. A spammer uses a server that bounces e-mails to distribute their spam by sending all spam e-mails to that server using the From: address field. Because they're invalid e-mails, that server would then bounce them back to the users who he/she wishes to spam and because the server is a legitimate server it wouldn't be blocked.
What can be done?
If your domain is configured to use catch-all addresses, which receive e-mail from addresses at your domain that are otherwise invalid, disable or limit them. Specifying what e-mail addresses are valid (e.g., [email protected] is valid [email protected] is not) can greatly reduce your amount of spam and bad bounces. If your ISP or web host has an online Control Panel (e.g., cpanel) you can adjust this setting through it. Otherwise, you'd need to contact your ISP or web host to have this changed.
If you are using a generic online e-mail service (e.g., hotmail) or an e-mail address from your ISP unfortunately there really isn't anything that can be done to prevent receiving these e-mails. Our best solution would be to filter or setup rules and policies for incoming mail to automatically delete these messages.
Has my e-mail address been stolen or hacked?
No. As mentioned above, it is likely your e-mail address is only being used by a spammer to help get around spam filters. When spoofing an e-mail address, you don't need access to the e-mail address account, the person sending the e-mail tells the e-mail server that it is coming from your e-mail address.
If you still think your e-mail has been hacked see our e-mail address has been hacked document.
Do I have a virus?
Not likely. As mentioned above, it is more reasonable to believe that your e-mail is being used by another spammer without any knowledge if that e-mail is valid or not. If you're concerned about a virus infection though, it never hurts to scan your computer.
ISPs and users running a spam filter or mail server
If you're running any spam filter or mail server, we strongly suggest that you do not bounce back any spam e-mail, virus infected e-mail, or invalid address e-mails.
If you're running a mail server and want senders to know the address is invalid, reject the e-mail during the SMTP transmission instead of bouncing the e-mail after it's been received. Rejecting instead of bouncing e-mail could save you, your server, and other Internet users lots of time and headaches in the future.