How to open P7M attachments – What are they?

P7m file extensions, also known as smime.p7m files are encrypted emails (or “digitally signed” emails) that only show the header information and an empty message body. The attachment is the text of the encrypted message
In order to properly view p7m messages, the best solution is to download and install a P7m viewer ( go to this link to download the P7M viewer from a company called Cryptigo: . The install file is called: p7vsetup.exe. The company offers a 30 day trial that will allow you to open the P7m file and read the encrypted or digitally signed email with the attached document (usually a word document)

Note: If you try to go directly to the Cryptigo website you will end up on a japanese language website about eyelash adhesive (I am not sure why!)

Here is a screen shot of the viewer:

The Univ. of Texas has also a good explanation of the issue:

also read more about digital certificates here:

Read the following Microsoft KB article (913966) that contains a hotfix for Exchange servers to better handle p7m files

This is the Wikipedia information about SMIME standard:


“S/MIME (Secure/Multipurpose Internet Mail Extensions) is a standard for public key encryption and signing of MIME data. S/MIME is on an IETF standards track and defined in a number of documents, most importantly RFCs(3369,3370,3850,3851). S/MIME was originally developed by RSA Data Security Inc. The original specification used the recently developed[1][when?] IETF MIME specification with the de facto industry standard PKCS#7 secure message format. Change control to S/MIME has since been vested in the IETF and the specification is now layered on Cryptographic Message Syntax, an IETF specification that is identical in most respects with PKCS #7. S/MIME functionality is built into the majority of modern email software and inter-operates between them”

Click on the Wikipedia link above to read more about SMIME standard.


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