We have a problem, that if one user becomes mail, sometimes it happen, that he can see only a square box like this: 
in the mail instead of the cc recipient list. User thinks, that it happen, if his colleagues are using the reply to button, but not allways, and from all his colleagues. He receives the mail, but cannot see the other recipients in the cc, even not himself.
Do someone have a thogh what could cause this, and how to fix it?
Thank you!
Andras Simon