System mail being sent with From and Return-Path headers set to my ssh account

[shalako]

System mail and mail created by php scripts are being sent with From: and Return-Path: headers set to my ssh user account: shannon@<hostname>

Why does this happen?
Where can I change it?

In Administrator settings, email is set correctly to systems@<domain>

I have given user shannon sudo rights in /etc/sudoers. But why would that effect mail settings?