Thunderbird Unread Message Count Incorrect

As always fix at your own risk.  I am not responsible for lost data if these instructions do not work, or make things worse!

Background:  I have encountered quite a few instances where the unread count for a folder in Thunderbird was radically incorrect.  Sometimes clicking on the folder would make it better, sometimes worse.  When manually counting the unread messages they were much less than the number displayed in Thunderbird.

These instructions are based on Thiunderbird v.1.5 on Windows.  If you are using an older version I recommend that you upgrade.

Short instructions: The key is to delete the .msf files from your Thunderbird folder (they will be recreated) and then enable folder compacting. 

Long Instructions:
  1. Close Thunderbird
  2. Click on Start > Run
  3. Type “cmd” and then click run (It will open a new screen and you are probably already at: C:\Documents and Settings\loginID
  4. Go to: "C:\Documents and Settings\loginID\Application Data\Thunderbird"
    Typing this exact command should get you to the Thunderbird folder (on Windows): “cd  \Documents and Settings\%username%\Application Data\Thunderbird
  5. Run “del /s *.msf”  (Be careful! Running a delete command can result in significant data loss.  Only delete the .MSF files)
  6. Open Thunderbird
  7. Go to the File Menu > Offline > Offline settings
  8. Put a check on the box “Compact folders when it will save over”  The default (as I recall) is 100KB which is fine.  For convenience I tend to bump mine to 1000.

Erik Smith 2006
Licensed under the GNU Free Documentation License