How to diagnose an issue in which an Exchange recipient that is visible in the GAL may not appear in the offline address book.
How to Send As a Hidden Mailbox
Some end users in your Exchange Server environment may have a requirement to “send as” a mailbox that they also need to remain hidden from the global address list.
Resolving Anonymous Mail to the GAL with Exchange Server 2010
You may encounter an issue where the emails that end users receive show the SMTP address of the sender instead of the more friendly display name configured on the user mailbox that has that SMTP address.
How to Remove Mail Users from the Global Address List
In this tutorial I show you how to use recipient filters to exclude Mail User objects from a Global Address List.
Unable to Modify Default Global Address List
How to modify the recipient filter of the default Global Address List in an Exchange Server 2010 organization.