What is the best way to send and receive transactional email?

I run a web-app where I would like receive facebook style transactional emails. For example, send an outgoing mail with a dynamic reply-to address of the form reply+2a3b4b2a34@domain.com (2a3b4b2a34 is dynamically generated hash)

This is in order that people can respond to notifications by replying to notifying email itself (rather than coming to the app). Now this poses multiple potential problems

1) Currently, I collect all incoming email to update@domain.com using google-apps. I then pull it to my server using IMAP, and then parse the response. I am a little uncomfortable doing this because I wonder if google really wants to use its email service in this manner. Or if they might have an issue with me receiving thousands of emails on this address.

2) What is a good way to remove quoted text in the incoming email (so that I can only use the actually reply)

Ideally, I would like to use an external service that takes care of such transactional emails, and use my server only for things that directly pertain to my app.