Erratic system behavior is generally the sign that an in-depth virus check is in order.
On a more lenient note, it might be worth finding out if people are recieving protected mail. Indeed, the sender can specify that the mail cannot be printed - which prevents forwarding, printing and copying contents. It might have an impact on the ability to open attachments as well.
Pascal.
I've got nothing to hide, and I'd very much like to keep that away from prying eyes.