Files that contain the .p7m file extension hold encrypted email messages. The P7M file format is a container format and the contents and the attachments of the encrypted email message are enveloped into the encrypted P7M file.
Oftentimes a user must have a private key installed into their email client in order to open the P7M files that they receive. The private key will match the message's public key so that the user can open the P7M file. This private key is static and does not change so that a user does not have to enter new information to open each P7M file they receive.
The P7M file format implements the Secure/Multipurpose Internet Mail Extension standard (S/MIME).
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