If you're using an Exchange server as a Dir-Sync server and address list replication doesn't work properly, follow these suggestions for debugging the Dir-Sync mail update process. To make debugging easier, you can add the DWORD Registry value PauseKicksDX to the HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\ Services\MSExchangeDX Registry key. The Microsoft article "XFOR: Manual Dirsync with Exchange Server as Dirsync Server" describes how to add this value. Be aware that editing the Registry incorrectly can cause serious problems, so work carefully. You need to add this Registry key if you updated from Exchange Server 4.0; Exchange Server 5.x includes the Pause function.
In the properties of your DirSync Server object, select Copy administrator on outgoing messages and Forward incoming dir-sync messages to administrator. This configuration lets you receive updates from the requestor, as Figure A shows.
Be careful if you restore your Dir-Sync server from a backup. Reinstalling the Dir-Sync server stops Dir-Sync because the internal sequencing numbers Dir-Sync is using become unsynchronized. The Dir-Sync mechanism uses two counters: a requestor sequence number and a server sequence number. The server sequence number is more important because it tells the requestor whether it has missed any updates. The mechanism behind this process is similar to the mechanism of the Update Sequence Numbers (USNs) in Exchange directory replication operations.
If your Dir-Sync stops, you need only to compare the requestor's server sequence number with your Dir-Sync server's sequence number. You can find the requestor sequence number in the message mentioned in Figure A. If you open the message, you find the counter SRVSEQ=1, as Figure B shows. This value must be lower than the Dir-Sync server sequence number. You can find the Dir-Sync server sequence number in the DXA-Srv-Seq field in raw properties of the Remote Dir-Sync Requestor object matching the remote requestor. To access the requestor's raw properties, go to Connections in Exchange Administrator and find the Dir-Sync server object you created that hosts the remote Dir-Sync requestors. Select the remote Dir-Sync requestor object that points to the remote requestor that is out of sync and choose File, Raw Properties. If the DXA-Srv-Seq number is lower than the SRVSEQ number, simply increase it above the SRVSEQ value, and directory synchronization will work again.