What exactly is the receiving username/password required for

Hi All,
I have the ServiceDesk Appliance installed and trying to set it up.

I am now at Setup > Email > Server. Here in the "Receiving" section, what exactly do I need the "UserName"/"Password" for?

Can I use and existing username? or do I need a have a separate Username dedicated for the ServiceDesk?

Regards,
Yaser.