Error opening message in outlook

[Roger Roger]

Hi experts one of my user is facing issue opening mails from one particular user in his outlook
when he opens message he gets error.
Below is the error message, he is getting and he has even put his credentials.

This message with restricted permission cannot be viewed in the reading pane until you verify
credentials.Open the item to read its contents and verify your credentials
the permissions has given by the user to open the email to this user but still same issue. i am not sure but i think email has been encrypted. in this case how to open the emails

[#2]

This is an RMS/AIP protected message most likely, so the question is, is the client configured correctly to connect to the IRM server?

[#3]

how do i need to configure

[#4]

For starters you might want to tell us which kind of RMS service you have, as the steps will differ. If it is even RMS, as that's just an assumption on my end.

[#5]

we are not using RMS