New form of SPAM?

Factual Questions
1

In the last 3 days or so I’ve received several emails from “postmasters” saying that an email sent from my address was not received by some non existant email address that I’ve never seen before. Within this email is SPAM or some sort.

Is this a new tactic, or is somebody actually sending SPAM to other people under my address?

2

My WAG is that someone else had a virus that sent emails spoofing your address. Any mail sent to an invalid address would be bounced back to you.