When a Microsoft Exchange Server 2013 mailbox user tries to forward a meeting request that is from an external sender, Outlook Web App displays the following error message, and the user cannot forward the meeting request:
Error: You don't have the permissions required to send messages from this mailbox.
If the user sends the meeting request by using Microsoft Outlook, the user receives a non-delivery report (NDR) that contains the following information:
A problem occurred during the delivery of this message. Please try to resend the message later.
This issue occurs because the SendAs check encounters an exception.
To resolve this issue, install the following cumulative update:
2892464 Description of Cumulative Update 3 for Exchange Server 2013
Microsoft has confirmed that this is a problem in the Microsoft products that are listed in the "Applies to" section.