I want to filter my emails using the header X-Comment, which appears in some of my messages. I added a filter to do this (using the "Customize" option) and tried to run it on my inbox, but nothing happened.

After some reading online I found this comment on a bug report regarding this issue, so I repaired the folder (right click, "Properties", "Repair Folder") and tried again. Still no results.

When searching for the header using the advanced search, I also get no results.

I also tried this with some other headers like Precedence or MIME-Version just to be sure and got the same results.

Does anybody have an idea how to fix this?


I have had this same issue too and reached your question. To me, what "fixed" it was a thunderbird restart.

If I tried to 'run now' the filter, it didn't work at all. Then I closed thunderbird and all its child windows, checked whether there were no thunderbird process (using process explorer), then restarted it.

The different thing (that I think should not be related) was, instead of opening the filters and clicking "run now", I did the following: 1. clicked the folder (Inbox) for which I created the account, (Inbox from the account of course) 2. Clicked the menu button 3. Chosen "Message Filters" menu 4. Chosen "Run Filters on Folder" menu item.

As I had 33,000 mails on that folder, it then hung Thunderbird for a while and voila, the mails which matched that header all moved to the target folder.

  • I, too, had to restart Thunderbird after making a custom header filter to make it work. – David Spector Dec 23 '20 at 12:16

Well, the problem just went away. Even though restarting Thunderbird did not help, the filter works just fine today (after rebooting Windows, so that may have helped).

I noticed that a new email was correctly recognized by the filter which prompted me to have a closer look again. I had to repair the folder another time, but now it works like a charm.

Who knows what changed..

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