Quick Thunderbird Tip: Repairing Mail Summary Files

English: Mozilla Thunderbird (SuSe Linux 9.3/K...
Mozilla Thunderbird (Photo credit: Wikipedia)

Couple of weeks ago, my Thunderbird mail client stopped connecting to Yahoo Mail. It would log in to the service, start downloading Message 1 of X — and hang. When it snapped back to normal, it reported there was no mail to download. Hmm…

After a few false starts, I found an old MozillaZine forum post that pointed to the Mail Summary File as the culprit. The MSF generates the list of emails on your Inbox, with date, time and read/unread status. The forum post said Go to your profile and find any files with an *.msf extension. Delete them, it said. So I did.

This turned out half-right. See, I like to think I’m pretty well-organized, with a bunch of topic-based folders and filters that move mail into those folders. Thunderbird (rightly) produces MSF files for each of these folders. When you delete them all, Thunderbird has trouble downloading into possibly nonexistent folders and it complains intensely.

For this reason, more recent versions of Thunderbird has a Repair function in the Properties of each folder. This tool reconstructs the Mail Summary File without having to drop the original. How do you do that?

  1. Right-click your Inbox and choose Properties from the menu.
  2. Click Repair Folder. The folder display switches to the cover page while the Repair tool is active. Depending on the size of the folder (and/or what the problem might be), this can take some time. Don’t try clicking on the folder until the repair is done.
  3. When the repair is complete, you’ll return to the message list, with the proper number of Unread messages counted on the left side. You can then click OK to close out the Folder Properties table.

If you still have trouble with downloading mail, or processing filters, try running this Repair tool on other folders.

Hope this is helpful.

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