Help: Problem with sending emails/From

[VB Programmer]

I have a few email accounts which I check with Outlook 2003. Example:

1. (e-mail address removed) (default)
2. (e-mail address removed)
3. (e-mail address removed)

Whenever I used to send out emails, the "FROM" would be my default, which is
(e-mail address removed). I recently added (e-mail address removed) to the list.

I noticed that all of a sudden I was getting "undeliverable" messages, to
people I always email. I took a look and the "FROM" address was the
(e-mail address removed) address (even though it was not set to default). I
deleted the postmaster account and sent an email and noticed that the "FROM"
address used the (e-mail address removed). I deleted that one, so all I had left
was (e-mail address removed), and now the FROM is BLANK! I deleted/re-added the
account several times and the "Test Account Settings" works perfectly. But,
when I send a message normally, the FROM is blank.

Any ideas?

Thanks in advance!