Microsoft 365 has many built-in controls to manage how users communicate externally, however, these controls do not generally extend to internal communication. While this is fine in most environments, situations exist where a degree of separation is required to segregate communication across different groups of users. This article details the configuration of Address Book Policies, and how they can be extended to include Teams.
How to diagnose an issue in which an Exchange recipient that is visible in the GAL may not appear in the offline address book.
Some users in your Exchange environment may have a requirement to "send as" a mailbox that they also need to remain hidden from the global address list.
Outlook users see the SMTP address of anonymous senders instead of the more friendly display name that appears in the GAL for that sender's email address.