Mime attachments kopano

When I receive an e-mail with an attached file with the extension .p7m in the message I see the symbol of the attachment but I can not open it.

Hello @f.pigliacelli,

since this is not directly Univention related I would suggest to rather post your question over at the Kopano forum. There the developers of the WebApp also check in on a regular basis: https://forum.kopano.io/category/21/plugins-for-kopano-webapp