Gargoyle's Message Rules for Outlook Express may be helpful IF you use Outlook Express. I can't say how similar other email programs may be.
From the original posting:
The Mrs. Freightdawg received an email as a "re:" in the subject line.
The "Re" in the subject line means that it is a reply to an email you sent. It should be followed by the original subject that was on the original email. Some email program setups will add a new "Re" each time the same message is sent back and forth, so a back-and-forth correspondence on a single subject can end up with "Re: Re: Re: ... Re: Original Subject." Some programs, with some setup options, can be made to terminate the number of "Re:" repeats at one or two. A common setup adds "Re:" for the first reply, "Re:Re:" for a response to the replay, but won't add more for Re: prefixes for subsequent passes. Some programs allow you to limit to a single Re: regardless of how many "passes" the same message (with additions) has gone through.
In effect, the "Re" means that the sender's address contained in the original email was used for the recipient of the reply, and the recipient of the original message would be shown as sender for the reply.
The "Fwd:" in a subject line is similar, meaning that the recipient of an original email is the sender but a new address is the recipient of the Forwarded message. Your setup determines whether you may see just "Fwd: Original Subject" or "Fwd: Fwd: ... Fwd: Original Subject." A lot of "friendly junk" mail of the kind that people receive and "share with all their friends" may be received with long "Fwd: Fwd: ... Fwd: " heads on the subject line.
The appearance of the Re: or Fwd: is not, in itself, suspicious.
rolled the cursor over the sender's name and the sender's email address showed up - and it was the sender's name followed my the Mrs. Freightdawg's
Rolling the cursor over sender's name does not show additional info in my OE setup, but that may work with your program. Since the Re: means that it's a reply to something you sent, some programs may show, separately, the current sender who is replying and the original sender of the message. I haven't seen it displayed separately in the manner described, but the information to do it that way is contained in the message.
You can look at your email program, and it's setup, to see if it's reasonable that when your address is shown for this email, it has the meaning that you were the originator of an email to which a reply is being made.
As to how someone can get (and steal) your email address, if you receive an email newsletter that uses "open addresses" in the "To" box (many addresses are shown), in OE and presumedly in most other email programs, when you receive an email you can one-click "Add to Address Book" and can choose "Sender" and/or "Recipients." If the email contains many addresses from a prior couple of Fwd: cycles, this will add every email address this particular missive has ever been addressed to into your address book. You can then, as described above, pretend to be anyone in your own address book when you send a new message (illegally, of course).
I've received "newsletters" and "joke Fwd:" messages that individually provided me with as many as 100 separate email addresses each of people I don't particularly care to know, had I wished to "harvest" them.
If you're receiving mail of this kind, you must assume that everyone else receiving the same email knows your addy.