Address Rewriting doesn't appear to work?

Afternoon,

following the examples from https://technet.microsoft.com/en-us/library/aa997185%28v=exchg.150%29.aspx?f=255&MSPPError=-2147217396 it should be really easy to get the edge server to rewrite the domain on its way out but I can't seem to get it working.

New-AddressRewriteEntry -Name "Domain Change" -InternalAddress mydomain.co.uk -ExternalAddress newdomain.co.uk -OutboundOnly $true

I was hoping this would rewrite my email mike@mydomain.co.uk and change it through the edge server by this policy to mike@newdomain.co.uk

I have tried single recipients as well but can't get it to apply this rule.

The Transport Agent is running and confirmed by using Enable-TransportAgent "Address Rewriting Outbound Agent"

.: Lister :.