Returned Mail error messages for messages I havent sent.

Hello DREA,
 
Welcome to the Community Forum,
 
Sounds to me that this is called email spoofing.
 
E-mail spoofing is the forgery of an e-mail header so that the message appears to have originated from someone or somewhere other than the actual source. Distributors of spam often use spoofing in an attempt to get recipients to open, and possibly even respond to, their solicitations. Spoofing can be used legitimately.
 
If you face this situation, your first step should be to determine whether your email account--or your PC itself--is infected or compromised in some way. The most likely culprit is "spoofed" email headers, in which spammers change an email header's "from" address to make it appear as though the spam originated from your email account, and which in turn causes any bounced email alerts to go to your inbox.
 
There isn't much you can do. You can change your password to your email account. Contact your ISP. You can delete your emai account and start a new which you may not want to do.
 
You can reduce your email account's exposure. For instance,  use your primary email account to communicate only with people you know and trust. If one of those contacts gets infected or compromised, attackers may still harvest and use your email address, but the risk should be much lower.
Also, when sharing an email address with a website or posting information in a public online forum, use a throw away account such as one from Gmail or Hotmail, that you won't mind deleting later on. There's simply no fool-proof way to prevent spammers from using your email address in spoofed message headers on spam email.
 
 
Hope this helps,
 
Kind Regards,