New Active Directory users are not found in the Spamfinder.
The Spamfinder accesses the Active Directory only when the Recipient Check is activated. Check this setting under:
Configuration -> E-Mail Transport -> Local Domains -> double click the respective domain -> LDAP Tab -> Recipient Check
The user is entered in the Spamfinderr when either:
* the user logs in to the User GUI the first time, or
* the user receives an e-mail via the Spamfinder.
The problem could also be that the replication of the Domain Controller has not finished.
Look in the logfile for any error messages and further information.