Notes/Domino 6 and 7 Forum : server trying to send directly to other server instead of using hub server

Hi, I'm sure this will have been asked before but I can't find it in a search or in the help.

Situation is that there are 4 notes servers servers in the same notes domain.
server A is the only one that communicates to all of the others so has connection documents to Servers B, C & D. Server A has notes domain /acme

Server B, C & D only have one connection document each to server A.

Server B is GB/acme
Server C is /acme
server D is de/acme

Server A is not set up as a pass through server.

I can send an email no problem from C to A & D and from D to A & C but I cannot send an email from D to B. Looking at the console, a mail going from D to C gets forwarded on to server A but a mail from D to B trys to connect straight to the B server when it should forward it on to A.

I've searched through all of the configuration documents but cannot see anything where you can tell it to forward all mail to the hub server (not relay as that is only for mail outside the notes domain). I thought at first I'd need to set it up as a passthrough server but the fact that its working for sending from D to B suggests there is a configuration line somewhere.

I hope I've not been too confusing with my post. Thanks in advance for any replys.