I suggest this:
1. Activate your MACID and email services through MUGSI
2. Switch to using Gmail if you haven't aleady
3. Set up your McMaster email to forward to your Gmail and delete its copy
4. Set up your Gmail to SEND from your McMaster account
Now, you will receive all your McMaster email and personal email through the nice pretty Gmail interface, AND you can send email from your McMaster address without leaving Gmail and using the terrible MUGSI interface.