XGS Email SMTP File protection problems with S/MIME Mails

Hi guys,

we have problems with SMTP File protection and S/MIME mails.

File protection is active and configured with Block file types "ALL". MIME white list is configured.

Now, external S/MIME encrypted Mails are getting filterd:

ontent-Type: text/plain;charset=UTF-8
Content-Disposition: attachment;
        filename= "filtered_smime.p7m.txt"
Content-Transfer-Encoding: base64

I cant find mime types for whitelist, all manual added mime types are not working... 
File types - Sophos Firewall

Manual mime types for whitelist:

Sophos XGS3300, SFOS 19.5.1 MR-1-Build278