Importance is a priority not a tag

In the write windows if you look on the Options menu you will see the menu entry for priority, but that does not help you as that sets it for the mail your composing. Corporate types and those from the Indian sub continent appear to love setting their mail to highest priority. They don't appear to get the fact I set priorities in my mail.

Try going on the toolbar then  once in the add-on manager type priority in to the search box and install the priority switcher. add-on. It looks like it will do what you want.

I'm not sure about tags as such, but I have had similar problems with junk messages in an Outlook account. If I mark a message as Junk, which moves it to the Junk folder as expected, then after a few seconds it reappears in the Inbox. As often happens, Microsoft thinks it knows better than you.

In my case, the best solution I have found is to move the offending message to the Junk folder in Local Folders, beyond the grasp of the IMAP-connected Exchange server. I suspect that if you move the "important" message to a folder outside the Outlook account you too will regain control of your own destiny.

Matt, thanks very much, that sounded promising but unfortunately doesn't solve my issue. i found and installed the add-on. A couple notes:

• When I use the add-on on one of these messages, it does show priority "Highest", but whether I choose "None" or "Lowest" or "Reset" the message simply disappears for a second, then comes back in its high-priority state.

• Perhaps Thunderbird takes the liberty of tagging the message "Important" based on the Importance or X-Priority headers, because the UI is indeed displaying it as a tag.

As Zenos said, we are dealing with server software that knows better. what is happening is your changing the mail and exchange is going no way. and changing it back.

Just to be sure, move such a message to a local folder. Then try the change. I think you will find the change sticks

Ah well. Thanks for the reality check.