Worm bait?

[Stephen Anthony]

I received a email from a postfix mailer that tells me the message I
sent bounced. All well and good, except I didn't send the message to
begin with. Also, it says it was sent from my old attbi.com address
(correct user name, tho) which I haven't used in a few months.

I'm running my Evolution as my mail client, if that matters. 

I'm concerned that someone may have gotten access to the attbi account
and is sending mail as me. 

Things I should do to investigate?

TIA,

Steve