You may receive bounced mailer daemon emails, often as incoming [SPAM] messages or undeliverable emails. This is not something to be alarmed about. This is unfortunately a common spammer tactic. The spammer is listing your email in the "reply to" field of their mass sent spams, when a portion of those spams are not delivered (bounced) they are sent back to your account as if you have sent them.
Your email has not been hijacked etc, it has only been used as an address to hide the real senders information. Your email is most commonly found by scanning websites or hacked and gathered from third party directories etc that you may have applied to.
Unfortunately there is nothing you can do except change your email address or create a rule to trash those messages.
