Your Yahoo! ID and part of your email address are listed on the Members page.

Anyone clicking on your Yahoo! ID goes to that ID’s Yahoo! Profiles page, which shows whatever information you’ve added — if any. A click on your partial email address allows other members to send you an email, without them seeing your whole address.

If you post a message — which sends each Group member an email — your entire email address is shown in the "From:" field, just as if you were sending them email directly.