How does automatic ride matching work?
If you check off the "E-mail me if there's a match for my ..." option, then as soon as anyone posts a new ride of the opposite type on the same date between the same locations, you will receive an e-mail alerting you that there's probably a ride offer/request of interest.
For example, suppose you are looking for a ride from Amherst to Boston on November 22 and returning on December 1. You will be notified as soon as anyone offers a ride from Amherst to Boston on November 22, a ride from Boston to Amherst on December 1, is returning to Boston from Amherst on November 22, or is making a return trip from Boston to Amherst on December 1.
Basically, any ride posting that satisfies any part of your trip will be brought to your attention.