You may email the requester from inside the Travel Tracker trip request. 

Open the trip request and scroll near the bottom where you will see "Send Email".

This opens up an email box for you to begin your email to the requester.

Once the email has been sent you will see it logged in the History log.  

You will also see the email in the Email Audit Log.  This gives you a snapshot of the actual email.  You may see this by clicking on the envelope next to "Email Sent by:"