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Thunderbird email database

Where are the Thunderbird email databases stored?

Thunderbird stores email databases in the profile folder which, in Windows, is located in the

 %USERPROFILE%\Application Data\Thunderbird\Profiles\XXXXXXXX.default\Mail\

  • Refer to the system tips for a description of %USERPROFILE% thing; you will also need to adjust Windows Explorer settings to show hidden objects - the Application Data folder is hidden from view with the default system settings.
  • XXXXXXXX.default - here X any letter or number.

Inside this profile folder you should find a subfolder for each your mail accounts and another one for "Local Folders". Each of those contains a bunch of files with the names matching your Thunderbird folder names.

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Thunderbird email storage format

Each Thunderbird mail folder is stored in two files named after this mail folder name:
  • File with no extension stores email messages in the plain text format, one after one. This file is larger than the MSF index.
  • A corresponding (smaller) .MSF file contains mail folder indexes and preference data. Thunderbird figures out what part of the message to be displayed, the order of messages within a folder, and the like - all based on the .MSF file information. It is important to note that .MSF files do not contain any email messages and, all in all, are redundant. Thunderbird will rebuild .MSF files as needed if they are missing.

What are Thunderbird SBD folders?

Folders with a .SBD file type (extension) are designed for a subfolder management; probably, SBD stands for SuBDirectory. SBD folders are used to hold a hierarchy of mail folders. When you create a new folder under some of the existing folder for the first time, Thunderbird creates a .SBD folder to store email data of this child folder. The folders are named according to the parent folder to which a child belongs.

For example, if you create a mail folder under "Inbox" folder, a message database file and corresponding MSF file of this child folder will be stored in the

%USERPROFILE%\Application Data\Thunderbird\Profiles\XXXXXXXX.default\Mail\Local Folders\Inbox.sbd

Zmeil email recovery software finds and displays appropriate message database files automatically.

Message folder size limitations

The total size of all the emails stored in a single folder cannot exceed 4GB. This includes any items deleted after the last compaction took place.
  • To compact a folder in Thunderbird, right click that folder and select "Compact" from a popup menu. This should be done periodically (once in several months perhaps).

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