The "Mail" folder, if you meant that one specifically is for Local Folders and POP-connected accounts. The filters for your IMAP-connected accounts would be in the account folders under ImapMail.

You are sure you selected the relevant IMAP-connected account when looking at the Message Filters dialogue?

A search for msgFilterRules.dat should discover all the filter files so you can check them for size and date last modified, but you would need to enable viewing of hidden files.

Yes, I've looked in the 2 IMAP and 1 POP account folders inside ....\Thunderbird\Profiles\y1drf32.default\Mail\Local Folders and ....\Thunderbird\Profiles\y1drf32.default\ImapMail\imap.gmail and gmail-1.com

Yes, I even tried changing the connected account- each of the three show 0 filters.

I did a search of my c:\Users folder and found the 3 msgFiltersRules.dat in each of the three folders per above. Each are a few bytes in size-

each file contains: version="9" logging="yes" and last modified date was today when I started Thunderbird.

BTW, the filters are still working perfectly today!

Strange?

Tried changing the default account in the Tools > filter dialog as Zenos suggested. It defaults to "local Folders"

Zenos said

A search for msgFilterRules.dat should discover all the filter files so you can check them for size and date last modified, but you would need to enable viewing of hidden files.

Not on Windows 10 Zenos. Windows has a seriously defective search. People trust is out of ignorance. Files in hidden folders are not searched, and at least on my machine if windows search is turned on for the profile folder things grind to a virtual standstill with the dreaded freeze for indeterminate period of time.

I switched between Local Folders and each of my accounts- still no rules. I just enabled filter logging so we'll see if that offers any clues. I can't manually run rules but they are running automatically when new mail arrives. And when the rule runs, the msgFilterRules.dat files is modified with a new new Date modified but the contents are just 2 lines; version="9" logging="yes"

If I add a new will it mess up my existing "invisible" rules? I really don't want to have re-type 30 + rules!

how are you viewing the contents of the files. Windows notepad? check that wordwrap is turned on. I have no idea as to the text encoding of the dat file. it may be using unix line markers so you just see something other than the whole message with the word wrap turned off.

Thanks for the replies Matt.

Notepad++. File size is 1 KB. 28 characters on 3 lines. Filter ran again fine today. Filter log is empty.

So I added a new filter (first one) to the other IMAP account and ran it manually. The filter ran. The filter log shows that it ran. And the corresponding msgFilterRules.dat has the rule saved in it. So it proves that the filter function is working properly. But not in the account that I really want to see/edit/add rules to.

Is there a tmp file somewhere I could look at? This is frustrating!

Have you actually restarted Thunderbird at any point in this process?

Ah...yes.