We are changing the behavior of how emails appear, when you navigate to a group in Outlook to make it similar to how your inbox or any other folder behave. With his change, users will have the capability to mark any email in groups as read or unread. The read state of an email inside a group would be maintained across sessions to enable users to leave a group and continue from where they left off.
Mailbox Plans allows the administrator to customize and pre-configure several mailbox properties that will be set on a mailbox at the time it is created. This feature extends the set of properties that are allowed to be configured.
Now you can see other people's responses to a meeting request, even if you aren't the organizer.
Office 365 allows up to 500 recipients on an email message or meeting invitation. However, if a meeting organizer sent an invitation to a distribution list (counted as only 1 recipient), attendees were added as individual recipients when they responded. So after more than 500 attendees responded, the meeting organizer could no longer update the meeting because there were now more than 500 recipients. We have made a first step in fixing this issue by no longer tracking individual responses (and therefore adding recipients) once there are 400 recipients. In a future update, we’ll track meeting responses in a separate property and use that when displaying attendee responses in Outlook.
Now when you create a group from the Exchange Admin center you can select to allow external users to email that group directly. - More Information