mdoerschlag

You could set a FollowUp.cc reminder on your emails in the Bcc field, and then it would remind you to FollowUp with them (or set up a filter to automatically Cc or Bcc FollowUp), but to automatically send on your befhalf, any software would need access to your inbox. Not sure if you're willing to give that info out.

seems like a less useful version of http://www.FollowUp.cc which has way more features and is still simple and flexible