When I add new users with the Microsoft Management Console (MMC) Active Directory Users and Computers snap-in, the users don't immediately appear in the Global Address List (GAL). What's causing this to happen, and how can I fix it?
The Exchange 2000 Server Recipient Update Service (RUS) generates email addresses. RUS also adds the Active Directory (AD) attributes that make the associated user account able to host a mailbox and make the mailbox visible in the GAL. If the RUS doesn't run, your newly created objects won't be visible. This problem is exacerbated by the fact that the RUS runs asynchronously on its own schedule, so sometimes newly created objects show up immediately, and other times it takes a while.
The first step in troubleshooting this kind of problem is to figure out whether the RUS is generating any errors. Check the event log for errors or warnings the MSExchangeAL service generates. Next, use ldp.exe or ADSI Edit to check a mailbox that should appear in the GAL and verify that its showInAddressBook attribute is populated. If not, the RUS isn't doing its job. If that attribute looks OK, compare the user object's USNChanged value with the msExchServer1HighestUSN attribute for the RUS on the server that hosts the user; if the USNChanged value is lower than the msExchServer1HighestUSN value, the RUS didn't update (or hasn't yet updated) the object. If the user's USNChanged value is higher than the msExchServer1HighestUSN value, the RUS might not have finished its work because it hasn't run yet. Run the RUS manually by right-clicking the Recipient Update Service object in the MMC Exchange System Manager snap-in.