Okay, to answer your questions.

Yes, the behavior is the same in safe mode.

I don't see a From button when replying or sending, as I only have one email account configured.

The email account is a pop3 account. I use a cable modem, and the email address is attached to my cable account. For the record, we get cable TV fine, I'm able to surf using browsers, and I'm even able to RECEIVE email. I just can't send any.

I read the link, and didn't see anything that helped.

Oh, and as an addendum, I can send messages to MYSELF and receive them just fine. Not sure what's going on, here.