For some reason, my Filter Log messages (there were two), have been garbled. Here they are again:

1)

[4/25/25, 12:35:15 GMT-4] Applied filter "Aeon magazine" to message from Aeon Weekly <support@aeon.co> - This week: Why AI science will be incomprehensible at 4/25/25, 12:34:22 GMT-4 moved message id = 89c6e02ebaf75bbc918731474.c3e7d573b0.20250425163412.c7ad5cda2b.7a1e170f@mail220.suw16.rsgsv.net to imap://mdalphin%40gmail.com@imap.gmail.com/Maillists/Aeon

2)

[4/25/25, 12:35:20 GMT-4] Filter action failed: "Move failed" with error code=0x80550009 while attempting: Applied filter "Aeon magazine" to message from Aeon Weekly <support@aeon.co> - This week: Why AI science will be incomprehensible at 4/25/25, 12:34:22 GMT-4 moved message id = 89c6e02ebaf75bbc918731474.c3e7d573b0.20250425163412.c7ad5cda2b.7a1e170f@mail220.suw16.rsgsv.net to imap://mdalphin%40gmail.com@imap.gmail.com/Maillists/Aeon

just a guess, but I think you will find the path imap://mdalphin%40gmail.com@imap.gmail.com/Maillists/Aeon does not exist in the profile you have copied the file to, hence the need to restate the location the filter is to use.

Thanks fro the reply, Matt.

I know that the path does exist because of two things. 1) This is an IMAP account and I used the filter on a different host, previously moving emails to the "missing" IMAP folder and 2) when a SNAP install wipes out my profile on a single host, re-installing a copy of the msgFilterRules.dat file has _all_ 31 move commands fail. That is: with a new version of Thunderbird already set up to download messages from the IMAP account and showing all the dozens of folders that I maintain, and with Thunderbird not running, I replace the existing, empty copy of msgFilterRules.dat with the older, previously working one where all 31 filter rules worked as expected, leads to ALL of the "move" action filters reporting non-existent folders. Note the lack of change in the IMAP account; all the folders are still there.

Perhaps there is a semantic issue here for "folder exists" or not. I know that I need to "subscribe" to folders under IMAP or they don't show up. Perhaps this relates somehow to that subscription process?

I just checked my subscription status via a right-click within the folders window and a folder that just failed for a "move" action (a pop-up message reported the failure and at the same time, the filter was disabled), showed a check-mark under the subscription window; I am subscribed to that folder. I wonder if Thunderbird does not internally keep track of these subscriptions or rather if there is a disconnect between the subscriptions shown in the folders window and the subscribed folders known to the filter mechanism? Alternatively, perhaps Thunderbird keeps an alias name to the IMAP folder (something kind of internal ID for disambiguation?) and when changing hosts or profiles, those internally used names change?

Certainly it would relate to subscription, the folders do not exist locally until you subscribe to them and filtering is done on local folders. The sync happens later.

Perhaps just dump the snap version and use DEB instead. They do not have anywhere near the issues the SNAP ones do. Probably related to the sandbox that snap enforces but it is SNAP users that keep appearing with issues after the Ubuntu change to SNAP.

I will call this "solved" but I am dissatisfied in that my use case of: "copy my mail filters between hosts" still requires substantial extra work to get the filters to work. I see the issue of subscription to folders - I wonder is there an "update" all subscribed folders or "sync" all subscribed folders button so that the subscriptions are up to date and accessible to the mail filters? Is that even possible? I already know that installing Thunderbird on a new host, connecting it to Gmail and letting it synchronize to my ancient IMAP folders takes a very long (>30 min) synchronization time and when that is done, most of the folders remain non-synchronized, requiring that I view them before the mail headers are downloaded.

As for SNAP, I have already adjusted Firefox to download directly from the Mozilla repo and I download the tar.gz of Thunderbird for installation in /usr/local/. The general damage to functionality for me caused by SNAP is just not worth the convenience of the Canonical easy binary download.