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Clients cannot connect to Exchange

I ran into a problem this week that caused a lot of headaches. In an existing Exchange environment everything seems to be working just fine for existing users. The problems occur when you try to configure an account on a new client. This scenario did not apply to all the mailboxes in the organization.

These are some of the messages that were presented during different stages in the configuration:
Outlook cannot log on. Verify you are connected to the network and are using the proper server and mailbox name. The connection to Microsoft Exchange is unavailable. Outlook must be online or connected to complete this action.
The name cannot be resolved. The connection to Microsoft Exchange is unavailable. Outlook must be online or connected to complete this action.
The action cannot be completed. The connection to Microsoft Exchange is unavailable. Outlook must be online or connected to complete this action.
Your server or mailbox names cannot be resolved.
The environment is a pure Exchange 2007 and we removed the last traces of the earlier Exchange 2003 just a couple of months ago. The first theory was that this had something to do with the problems, but it seems like it did not. There has also been a lot of things happening in the Active Directory environment because we are preparing for a 2008 R2 upgrade.

Finally we to found that similar problems might occur if there are any issues with the System Attendant service. The Microsoft Exchange System Attendant is a service that runs on the Exchange server and works like a proxy to the Active Directory for some functions in Exchange.

The service seemed to be working as it should, but after I restarted it everything began to work. I still have not found any logs to identify the cause of the problems, but at least we got everything working.
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