We have an Exchange 2010 and an old Exchange 2003 in our org.
I moved all the resource mailboxes from the old exchange 2003 to the new exchange 2010 and some users as well.
Everything runs ok, with the only thing that some users who wants to send mail from these shared mailboxes are not allowed to do this.
This happens only if they try to do it from an Outlook 2010 client
If they do the same thing but from an outlook 2003 client then works.
Extra info : both user and resource mailbox are in the Exchange 2010 maibox server
Any ideas ?