re-creating the edge sync subscription exchange 2007

symptoms:
new users can't recieve external emails

When you attempt to telnet to the edge server and send an email to a new user the server will respond that it doesn't know who that user is or something similar

causes:
the edge sync subscription has stopped working
this can be due to different patch levels or update rollups on the hub and edge servers
you need to have your exchange servers on the same patch levels

How to confirm:
1. Run Adsiedit.msc
2. Navigate to Configuration->Services->Microsoft Exchange->Organization Name->Administrative Group->Exchange Administrative Groups->Servers->Edge Server Name
3. Right click the Edge Server and click Properties
4. Locate the msExchEdgeSyncCredential property. Does this have a value set? It will probably show as not set.

solution:
re-create the edge sync subscription

preperation:
Do a full backup on all exch servers if you can.
You must backup all exch databases
You must backup system state on all servers
You must back up how your send connectors are configured (screenshots)

implementation:
On the EdgeServer start up the Exchange Management Shell and type:
New-EdgeSubscription -file “c:\subscription.xml”
Browse to the root of C:\ and copy the subscription.xml file to your hub server. This can be tricky sometimes due to the Edge being located on a DMZ or inaccessible network. I used a USB key to move it between both servers.

On your Hub server open up Exchange System Manager and add the new subscription:
Organization Configuration> Hub Transport> Create New Edge Subscription.
Browse to your subscription.xml file and then click New.  Make sure that your subscription is set to the correct site. It will choose Default site as default, so don’t just click next, double check that it is being subscribed to the same site as your Hub server.

NOTE - You do not need to remove the existing Edge Subscription. The new subscription will simply overwrite the existing one as it is for the same servers.  

We now need to replicate Active Directory information and synchronize the Edge and the Hub server.
In Exchange Management Shell on your Hub servers and run the following command:
Start-EdgeSynchronization

Hopefully this completes successfully and you should now have a working Edge Sync.

To verify that it is all working as it should, run on your Hub server:
Test-EdgeSynchronization and you should receive a status of succeeded:

Some people have found that re-creating the EdgeSubscription resets your send connectors, but I have not come across this. The settings within the Send Connector and SPAM setting etc, will stay the same as we have not removed the existing Edge Subscription, we have just overwritten attributes within it. Just in case though, verify your Send Connectors with the settings you recorded at the start of the EdgeSubscription process.