Getting bounce back e-mails from addresses I don't know
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.
3. A spammer may use your domain name to help generate fake senders of e-mails. For example, firstname.lastname@example.org, email@example.com, firstname.lastname@example.org, etc.
What can be done?
If you have your own domain name that has unlimited e-mail addresses, sometimes referred to as "catch all", limit it. Specifying what e-mail addresses are valid (e.g. email@example.com is valid firstname.lastname@example.org 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 just 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.