Direct emails

Looking for some guidance.

We have an email address of servicedesk that is used for our email service. If a new ticket is entered the confirmation comes from that address and it looks like we also use it for replies which is probably problematic.The issue is that people are slowly starting to try emailing that address directly to circumvent using the portal and there message ends up in the unsuccessful as it doesn't have a reply token. I guess I have a two questions:

1. Do we need to setup a separate reply to address for handling comments on tickets to separate the two different requests?
2. Is there anyway to have it so if a person emails the servicedesk address directly that they would receive an email instructing them it's an unmonitored account and I assume that would be for our exchange team to setup?
3. Am I way off the mark on how to address this issue? :)

Thank You,

Kevin