Group Posts Via Email Now Support Non-Unique Email Addresses
Starting in Spring ’15, Chatter groups support posts via email from non-unique email
addresses in your organization, as long as they’re unique at the group level.
Previously, email addresses shared by more than one user record were blocked from posting to groups. Going forward, posts from such email addresses will not be blocked. Of the multiple user records an email address is associated with, posts to the group feed display as posted by the user record that is also a member of the group. If multiple user records that share email addresses are members in the same group, then posts from that email address to that group are blocked.