Smart P7M Support For Mac Publisher's description
from Paolo Kaosmos
"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.
Teorically Thunderbird should automatically verify signature and show attachments in postive case; if the verify fails, attachments are hidden.
Unfortunately this verify seems not work properly in some cases, even if you import new certificates.
What's New in This Release:В· compatible TB 1.5-9 / SM 2.0-2.4
System Requirements:В· Thunderbird 1.5 to 3.1
В· SeaMonkey 2.0 to 2.1
Program Release Status: Minor Update
Program Install Support: Install and Uninstall