Create a new ticket in Request Tracker via gmail or public mail

Question

I have basic knowledge in RT. Created a new ticket in Request Tracker via email.

I have installed RT and configured sendmail. I have used my Gmail account username & password for outgoing server. It's working fine.

I want to create a ticket from via email. I have used RT-mailgate. I have mentioned below entry in /etc/aliases.

rt: "|/opt/rt4/bin/rt-mailgate --queue general --action correspond \
    --url http://rt.example.com/"
rt-comment: "|/opt/rt4/bin/rt-mailgate \
    --queue general --action comment --url http://rt.example.com/"

Where do I have to configure my incoming server details and how?