Thanks, guys. Yes, I thought that if my account was being used for spam that I would have had hundreds or thousands of bouncebacks, but I've had just the one. I'll delete it, as advised. Funny, but the address I supposedly sent to is very similar to mine, such as:
if my address is
jsmith@johnsmith.com
the address supposedly sent to is
jjones@johnjones.com
IOW, same first name as mine, different last name, at full name dot com.
I'll just delete it.