Does this affect all received messages?

I tested sending from 3 different addresses (all my accounts within Thunderbird). It handles them all the same.

Aha ! A clue ! When I respond to outside messages, it handles them fine. Just those sent from my accounts within TB.

???

So still.. how can I get TB to behave and switch back * the TO: field and FROM: field, for message sent from different email addresses within TB??

What do you mean "from your accounts in TB" how are these different to "outside" messages. I think therein lies the clue.

Exactly! We have the clue, but not the solution. When some friend writes to me and I REPLY, all works fine. But when one of my 5 own accounts set up TB (Thunderbird), it reverses the TO and FROM.

   WHY? How to fix?

1. e.g. If I write an email From: OldOne To: DaveNew, when I open the email at DaveNew and hit REPLY, it automatically sets up as From: OldOne To: DaveNew, instead of a reply coming From DaveNew.

2. Note: This only happens in my brand new DaveNew account (and 2 more I just set up last week) . If I go to my Cpanel in my Hosting account, the Webmail behaves fine. The problem must be in TB.

3. Also, my other email accounts (e.g. OldOne) do not mis-behave like this.

4. On email from others the reply setup works properly, within DaveNew.

5.I checked the DNS settings to make sure they are kosher, re-started TB, restarted Windows, etc. No dice, so far.