A P7Z file is a compressed file that contains an email message in the S/MIME encryption standard. It was introduced by Microsoft Corporation and is categorized as Email related data file. P7Z files have application/pkcs7-mime media type. It contains one or more parts of a message that is compressed with zlib compression algorithm.
P7Z File Format - More Information
The internal file format details of P7Z file format are not known. Some APIs such as Aspose.Email lets you read the S/MIME part of the messages. If an email client does not have the capability to handle the compress data, compressed S/MIME messages come as email attachment.