WM5 Device connect to Exchange and send but doesn't seem to reciev

Folks,

I've been pulling my hair out with this one for weeks now. Apologies if this
problem has been raised and solved earlier (had a quick look with no joy)

We're running Small Business Server with Exchange 2003 SP2. We've got a
number of new Orange SPV M3100s (HTC Hermes?) running WM5.

I've managed to setup the Exchange ActiveSync connection and use
'home-grown' certs to get the device connecting over the air to the server
(and locally) and 'apparently' syncing. New items on the device are added to
my exchange account but the device never downloads the exchange items (mail
etc.). i.e. I can send mail from the device but not recieve, additionally
once its sent it does not appear in the sent folder on the device....

From what I can see all the virtual directories are setup right and we are
not using URLSCAN on the server (could block headers) ... any thoughts would
be greatly appreciated... Basically the device thinks its connected and
working OK but it isn't.

Couple of notes:
1. I've tried syncing with a third party hosted exchange server and it
worked perfectly... i.e. theres something wrong on my server/network setup
2. We ahve 4 devices in the company and all are having the same issue - as
does the MS emulator which I have tried as well.