In oups.com,
typed:
I run both Outlook and Thunderbird at home and at work. Outlook 2003
at work, and Outlook 2000 at home.

Whenever I send an e-mail from Thunderbird to Outlook 2003, Outlook
2003 sticks the e-mail in the junk folder. This includes e-mails I
sent to myself, to others in my company, and to outside B2B sites I
use. As far as I know, it's 100% of my e-mails sent.

I have modified Outlook 2003 at work so that my domain is on the safe
senders list on all my users PC's using the safe sender import
feature. Obviously, I can not do this outside my company.
But this doesn't completely solve the problem. Even though I have
junk e-mail filtering turned to "no automatic filtering" and I have
whitelisted myself, I still see my own e-mails to myself going into
the junk folder.

Am I alone in this issue, or is this known & have a fix?

Perhaps this is being done on the mail server....such as Exchange. If so,
take it up with whomever manages the mail server....it doesn't seem to be an
Outlook thing, since you've disabled your own junk mail filtering.