Mozilla Thunderbird mail message file
File type: Email related data file
A .wdseml file is a mail message file created by Mozilla Thunderbird.
It contains message data associated with a Thunderbird mail account and profile.
File type category:
Email related data file
Date updated: October 6, 2026
The .wdseml file extension is associated with Mozilla Thunderbird, an email client from Mozilla for Microsoft Windows, Linux and Apple macOS.
A .wdseml file stores a copy of a Thunderbird mail message. Thunderbird can create these files for integration with Windows Search, allowing messages to be indexed and found through the operating system's search features.
These files are supporting files in a Thunderbird profile rather than the main mail store or a general-purpose message format. They may be encountered alongside Thunderbird's other profile and mail files.
Use Mozilla Thunderbird to view the message associated with a .wdseml file. In most cases, the original message should be opened from its mail folder in Thunderbird rather than by opening the supporting file directly.
Thunderbird is available for Microsoft Windows, Linux and Apple macOS. A .wdseml file created for Windows Search may not open as a normal standalone document outside Thunderbird.
There is usually no reason to convert a .wdseml file directly. It is normally a supporting copy used for message indexing, while the original message remains in the Thunderbird mail store.
To create a portable message file, open the original message in Thunderbird and use its save or export command, such as saving it as an EML file.
Software apps that create wdseml files:
Microsoft Windows
Apple macOS / Mac OS X
Linux/Unix
Software applications that handle other tasks involving wdseml files:
Microsoft Windows
Apple macOS / Mac OS X
Linux/Unix
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