Upload error with p7m files

Hello everyone,
I am experiencing errors when uploading files with p7m extension.

The Browser sees the files as "application/pkcs7" (tried both with Google Chrome and Mozilla Firefox), inside the file mimes.php instead are identified as "application/pkcs7-mime", "application/x-pkcs7-mime".

I tried to add the extension in the array but I always get the error: "The filetype you are attempting to upload is not allowed.".

I've done numerous tests, modifications, etc... but I still haven't found a solution.

Any advice/suggestion?