It would have been better to keep the original profile name, hence to rename 'aaaaaaaa.default' to 'bbbbbbbb.default'. Most likely, you now/still have references in the prefs.js file to the latter affecting your filters and possibly other settings, so they don’t work. It would also save you from renaming the profile in profiles.ini.

You can try editing the prefs.js file, but this is not advised so I’d do the above. If you add another profile using the Profile Manager just to create a new profile, exit Thunderbird, rename that and copy the entire content from the backup there, you can still do so without losing the current one.

_{/Edit: prefs.ini -> prefs.js}

Hello Tonnes,

I followed your recommendation and created a new (second) profile using the Profile Manager and copied the full profile contents (containing the non-working filters) into this new profile. When starting up Thunderbird again I got the question which profile I'd like to use and choose the new profile.

Unfortunately the 2 incoming messages I received today didn't which should have been filtered, didn't get auto-filtered by the new profile environment.

Is there a parameter in the profile which determines if auto-filtering should be done for all filters during start-up, or does Thunderbird check the auto-filtering option for each and every filter definition one-by-one? If the latter is the case it might be that the some filter definitions got corrupted (maybe not visible when outside the readible ASCII-range) and therefore aren't processed by Thundebrid?

I might have overlooked that you wrote "but my problem occured also on other computers with some older Thunderbird versions" and purely based the reply on the question title. In other words, I assumed the filters worked fine in your old setup when run automatically. It may be obvious that any issue in an old profile will be copied over when copying that entire profile (i.e. all its files) to a new one, while it should not happen for a profile that worked fine.

I’m not aware of issues with message filters right now. However, did you make sure the checkbox for Getting New Mail: at the top of each filter definition is ticked? If not, they would only be run manually, provided that box is ticked.

If you open the msgFilterRules.dat file(s) for the affected account(s) in a text editor (they reside in the profile’s Mail (for POP) or ImapMail (for IMAP) folder > <account name>), you could check for the filter types the messages are set to. For instance, if your filters are set up to be run manually as well as automatically when fetching mail, they should look like type="17". When unchecking the box to run them automatically (i.e. untick "Getting New Mail") and only checking "Manually Run", that type should change to 16. Make sure these types are actually 17 when both boxes are ticked.

Also, do you see anything in the filter’s Filter Log? And have you installed any add-ons that may be interfering and if so, did you try if the same happens in Thunderbird’s Safe Mode?

Hello Tonnes,

If have read your message, but due to busy work now and a short holiday next week I'm not able to verify your recommendations at this moment. Get back with feedback after next week anyway.