This is usually caused by staff having their PC rebuilt and an old Notes ID file being used in the process. As it’s old, it doesn’t contain the newer keys that would be required to decrypt recently sent emails. At a guess, the affected people have been with the company over 2 years, right? The other, relatively new staff, are unaffected.
It’s best to wait for your qualified Notes Admin to return for this, he should be able to resolve it. In the meantime, the sender should re-send the message without encryption.
– Which property are you checking to determine that the message is encrypted?
– What is the exact error message seen by those users who cannot read encrypted messages?
– Is it a specific set of users having this problem? Are they unable to read any encrypted email or just a selected set of encrypted messages? If problem is limited to a selected set of messages then do you know which Notes domain the senders reside in?