Hello Humphrey,

Request Tracker (RT) does not pop e-mails. It does not have such a function. You must have a running MTA on your server, besides finding another way to get/download those e-mails onto the RT server. You could use fetchmail or getmail, but such is not an elegant solution for RT.
RT's queues each require a unique address for correspondence. These addresses must be identifiable by your MTA if you need RT to interact with users.
So go ahead and install a functional Postfix/Exim (or your choice MTA) on the server and find a way for the MTA to handle e-mails to RT
If you intend to use Exim as your MTA, you can find configuration details for Exim on this link. This is only for the MTA. You still need to configure RT_SiteConfig.pm and Apache in order to get everything glued together and running.

HTH