Hi
I'm carrying out an Exchange migration for a client running Exchange 2003 previously and have come across an interesting problem.
In Exchange 2003, they have a number of mailboxes that they use to represent meeting rooms and to book a meeting room, people send an invite to other attendees and select the room mailbox as 'location' when sending the invite.
They had the issue of people putting the room mailbox in the To: field and to overcome that they set up delivery restrictions on the mailboxes representing rooms so they would only accept messages from 'Administrator'. This permission lockdown resulted in the sender getting an NDR if they addressed the message to a room mailbox by putting it in the To: field but not getting an NDR and booking the room correctly if they selected the room mailbox as 'location' in the meeting invite. Screenshot of delivery restrictions below.
This worked fine while they were on Exchange 2003. People have now started to migrate to Exchange 2010 as part of a migration pilot. When the Exchange 2010 users try to book a room using the same method of selecting the room mailbox as location, they see the mail tip "You don't have permission to send to <Mailbox Name>", but if they go ahead and send the invite, the room does get booked.
Even though the room booking is working, the mail tip is causing confusion so it needs to be made to go away.
My understanding of the problem is that what they have done is an unsupported configuration with Exchange 2010. Using the knowledge from the article http://support.microsoft.com/kb/2755743?wa=wsignin1.0, I believe what is happening is that Exchange 2010 is checking the sender's permissions to send email to the mailbox selected as location and displaying the mail tip stating they do not have permission and that is correct. However, because the room mailbox is selected as 'location' in the meeting invite, the room does get booked and there is no NDR, which leads me to believe that the invite to a mailbox selected as location is not sent from the actual sender but from the 'Administrator'. This is why the room gets booked but the user also sees the mail tip. Why the Administrator, I wondered. I'm guessing because it is the postmaster. Screenshot of mail tip below.
It is clear my understanding of this is not at a point where I know for sure how it works and how to resolve this and make the mail tip go away without changing the way the client works. They have about 60 different meeting rooms and over 700 users who will need to re-learn a daily task if we make changes to how the users book the rooms.
Much appreciate any help I can get on this one.
Thanks
Nauman.