Yahoo! Groups uses an automated system to test and reactivate email accounts that bounce. For that reason, there’s no need for a moderator to take action to unbounce members. It will happen automatically.
Note: There’s no negative effect on a group if it is has bouncing
members; it just means these members aren't getting group emails.
However, if you want or need to unbounce a member more quickly (the automated process usually takes between 3-7 days), moderators can immediately make a "Reactivation Request" for any member of their group (see below) and a user can make such a request for their own account at any time.
Automatic Reactivation
Yahoo! Groups periodically sends automated test messages to bouncing members. If a test message isn’t returned to Yahoo! Groups with an error, we assume the message was successfully delivered and automatically reactivate the member's account. This process doesn’t require any action by the moderator or member.
Manual Reactivation
To manually reactivate a member account for a group you moderate:
Note: The automatic unbouncing process can take several days before a
user is sent email again.
Unsubscribe Member
To unsubscribe bouncing members: