Our 2007 and our new Exchange 2010 servers were set with no limits. I currently have the active sync users still on the exchange 2007 Server. A couple of the users on the exchange 2010 server are not able to receive mail with attachments and I received an NDR from one of the senders which states the following:
The recipient's mailbox is full and can't accept messages now. Please try resending this message later, or contact the recipient directly.
I know that the mailbox is not full becuase you can see that there are no limits on the client mailbox.