I wanted to have certain emails forwarded to my Gmail account from my Exchange mailbox as they arrived, as email arriving in my Gmail account are pushed to my phone, not unlike a Blackberry. I soon realised that the rule was not working, and so did a little research.

What I discovered is that automatic forwarding to an external domain is disabled by default so I had to turn that option on. Internal forwarding is enabled by default.

To do this, open the Exchange Management Console, open up Organisation Configuration, select Hub Transport and go to the Remote Domains tab.

Normally there will be only one entry in the list, so select this and go to Properties.

Click onto the Message Format tab, and check the Allow automatic forward option, and click OK.

Now your forward and redirect rules should work to external domains!

TL;DR – EMC > Organization Configuration > Hub Transport > Remote Domain Properties > Message Format Tab > Allow automatic forward