We have a single new windows 2012 server running exchange 2010. We have 2 sites connected via in WAN, and all seems to be working OK, apart from this strange anomily. (The client is using Outlook 2010).
We have one user who wants to send an e-mail to another internal user from site 1 to site 2. simple e-mails work fine, but whenever he inserts attachments, the message does not reach its destination. The physical exchange server is at site 2.
"Delivery has failed to these recipients or groups.
You cant send a message on behalf of this user unless you have permission to do so. Please make sure you're sending on behalf of the correct sender, or request the necessary permission. If the problem continues, please contact your helpdesk."
The strange thing is that he is not sending on behalf of anyone, he is sending from his own mail account to another internal user.
Can anyone help resolve this issue.