If your AD synchronization for a company doesn't work (and others do).
It's most likely due to the configuration of that single company.
If you check the logs for the RfAdReplication service (should be installed on same server as domainmaster)
and find the following error occurring "ConnectToAd - A referral was returned from the server." It's probably the Domain Path on the company.
Ensure that you have entered the path correctly according to the AD integration documentation
- It can also be that you are missing a whitelabel/whitelisting of the emails domains,
you should ensure that you have added all domains for the desired email addresses
as shown in the AD integration documentation