Exchange 2007 Out of Office sent to Internet recipients with empty return path (Null Sender) e.g. "<>".

This behavior occurs because the OOF messages created in Exchange Server 2007 will be sent to internet recipients with empty return path (nullsender) e.g. "<>". Some third party Spam AV/Smart host does not accept messages with empty return path.

 

This behavior has changes since Exchange 2003 which send OOF messages as the OOF mailbox. The changes of the Exchange 2007 OOF behavior is because sending the OOF messages with no return path will prohibit the messages to bounce. As per RFC 2298 Message Disposition Notification (MDN) messages should be sent with blank sender. The OOF reply messages are an MDN.

 

To workaround this issue in this scenario, you can create Outlook rule to auto reply messages to instead of OOF messages, thus or configure the third party Spam AV/Smart host to accept messages with empty return path.

 

Note The Exchange 2007 edge server will not reject the OOF message as the edge server will be incorporated in to the Exchange organization. The HUB server will transfer the OFF messages in the address of OFF mailbox to the edge server and the edge server will then send the messages with empty return path e.g. blank sender, MAIL FROM: <> "null" to Internet.