Webmail sending as anonymous

Hi, looking for some advice on why a particular issue might occur

On occasions users have complained that email they sent via webmail didn’t get saved in their sent items

This happened over the weekend and I looked into it, and found that the email that got sent was sent by anonymous (from the user, sent by anonymous).

What I think is happening is that the user is writing the email for a long time, the session is timing out but the email goes out, sent by anonymous but doesn’t get saved as the access has expired.

On other occasions when the user times out he/she gets informed of this and they lose the email completely, which is a pain but more understandable.

Anyone know why the user might be able to send as anonymous?