With Yahoo! Groups, you can do a lot (subscribe, send messages, receive Group updates…and more!) purely with email. Here are some useful email operations:

• To join a group, send a blank message to:
  groupname-subscribe@yahoogroups.com
• To unsubscribe from a group, send a blank message to:
  groupname-unsubscribe@yahoogroups.com
• To post a message to a group, send your message to:
  groupname@yahoogroups.com
• To post a message to a group's owners and moderators, send a message to:
  groupname-owner@yahoogroups.com
• To put the group’s email message delivery on hold, send a blank message to:
  groupname-nomail@yahoogroups.com
• To change your subscription to daily digest mode, send a blank message to:
  groupname-digest@yahoogroups.com
• To change your subscription to individual emails from the group, send a blank message to:
  groupname-normal@yahoogroups.com
• To receive general help information, send a blank message to:
  groupname-help@yahoogroups.com

Please Note: Make sure to replace "groupname" in the above commands with the actual name of the group (e.g., pastry_chefs-subscribe@yahoogroups.com)