Smart P7M Support is a Thunderbird extension - build after lots of tests - that can "unhide" and handle P7M attachments.
P7M attachments are files with a digital signature that confirms sender's identity.
Since Thunderbird considers just the attachment type (content-type), it's more correct talk about attachments with type application/pkcs7-mime or application/x-pkcs7-mime.
In theory, Thunderbird should automatically verify signatures and show attachments in positive case; if the verify fails, attachments are hidden.
Unfortunately this verify seems not work properly in some cases, even if you import new certificates.
How to Install in Thunderbird;
1. Right-click the link below and choose "Save Link As..." to download and save the file to your hard disk.
2. In Mozilla Thunderbird, open Add-ons from the Tools menu.
3. Click the Install button, and locate/select the file you downloaded and click "OK".
· Mozilla Thunderbird
What's New in This Release: [ read full changelog ]
· Fixed compatibility with Enigmail + PGP.