How do you know the workstation that has sent a mail?

Hello

One user complains that there are someone who is sending mail with his mail account, because he sees mails sent apparently by him, but he hasn’t done it. So I suppose that someone has his notes id, a local replica or access to his web password. Do you know if it is possible to know from which desktop is sent a mail? ON the mail tracking I haven’t seen this information.

Thanks in advance