Mobile mailclient problem for one postoffice

[sindrehi]

Hi,

We have one postoffice where users now report problems with email on their mobilephones. There is several emailaccounts in the same postoffice, and all have the same problem. It is also on both android and iOS.
The problem is that email content is not visible. On Android there is a attachment named "unknown". On iOS there is a message "This message cannot be displayed due to the way its formatted. Ask sender to send message in another format or with another program"
(See attachments)
But it is happening with all emails. And it started last friday. Thuesday it was working, and friday not.
There is no other compaints from other postoffices on the same server. And there has been no server maintance / work on server in this periode.

Any idea what might be the problem here?

Best Regards,
Sindre