Internet, Networking, & Security Browsers Quick Guide to Repairing Folders in Mozilla Thunderbird By Heinz Tschabitscher Writer A former freelance contributor who has reviewed hundreds of email programs and services since 1997. our editorial process Heinz Tschabitscher Updated November 14, 2019 Browsers Chrome Safari Firefox Microsoft Tweet Share Email Sometimes, the folders in Mozilla Thunderbird lose track of the underlying structure—messages actually present are not shown, or deleted emails are still present. Thunderbird can rebuild the folder index, which displays the message list quicker than when the folder's full contents are loaded, and make it accurately reflect the messages you have in the folder. fotosipsak / Getty Images Repair Folders in Mozilla Thunderbird To rebuild a Mozilla Thunderbird folder in which emails have disappeared or deleted messages are stubbornly still present: Turn off automatic mail checking as a precaution. This may not be necessary, but it prevents a potential cause for conflicts. With the right mouse button, click on the folder you want to repair in Mozilla Thunderbird. Select Properties… from the menu that appears. Go to the General Information tab. Click Repair Folder. Click OK. You don't have to wait for the rebuilding to finish before clicking OK. However, you should not do anything else in Thunderbird until the rebuilding process is complete. Have Mozilla Thunderbird Rebuild Multiple Folders To have Thunderbird repair the indexes of several folders on automatically: Make sure Mozilla Thunderbird is not running. Open your Mozilla Thunderbird profile directory on your computer. Go to the desired account's data folder: IMAP accounts are under ImapMail.POP accounts are found under Mail/Local Folders. Locate the .msf files that correspond to the folders you want to rebuild. Move the .msf files to the trash. Do not delete the corresponding files without the .msf extension. For example, if you see a file called "Inbox" and another file called "Imbox.msf," delete the "Inbox.msf" file but leave the "Inbox" file in place. Start Thunderbird. Mozilla Thunderbird will rebuild the removed .msf index files.