My organization has been running Exchange Server 2010 for a few years now and we, only today, realized that it, by default, does NOT process incoming meeting invitation responses from invitees external to the server itself.
What does this mean? It means that our users have no clear indication that external invitees have even seen their meeting invites, let alone whether or not they intend to attend. Further, any changes made to the meeting invitation get pushed to all users, even if the “Send only to changed” option is selected. Consequently, we wind up unnecessarily spamming invitees.
This blows my mind – what the heck is Microsoft thinking?!
The good news is that it’s easy to configure either an individual mailbox or an entire mailbox database to accepting responses. The bad news is that there’s no way to configure this as the default behavior for newly-created mailboxes.
From the Exchange Management Shell:
Get-mailbox <alias> | Set-CalendarProcessing -ProcessExternalMeetingMessages: $true
Get-mailbox -Database "Mailbox Database" | Set-CalendarProcessing -ProcessExternalMeetingMessages: $true
Further, you can verify that the setting is enabled (last checkbox) by checking the details: