Yahoo! Groups created before April 2012 had the option for owners and moderators to bulk-add members through the “Add member” option. Unless such users explicitly link the email address used to add them to the group, to their Yahoo! profile, they cannot access the group via web. Many of these users remain email-only users of these groups.
Some of the users are surprised to see mails from a Y! Group that they have not chosen to join, but have been “added to”. This has been a cause for concern and many user complaints, as this provides an option to add member to a group without users explicitly choosing to join the group.
We are removing this option with immediate effect. This might cause some inconvenience to moderators that may be using the ‘Add member’ option. The change is done in response to customer concerns on potential abuse. The “Invite members” option is available as always, with a reasonable limit on number of users that can be invited in a 24 hour period.
– Yahoo! Groups Product Team