Microsoft Exchange user information is stored in Windows Active Directory (AD). The “display name” of each mailbox user in AD is used as the display name of email addressed to or from the mailbox. The default format for display names in AD is “Firstname Lastname” (first-space-last). The display name is used by the Outlook Global Address List (GAL) as well as in the header fields of individual emails.
The default display name format can be changed so that new users will conform to your standard template. For example, you could use a format like: “Lastname Firstname MI” (last-space-first-space-middleinitial). Instructions are available to change the default name format, and also retroactively reformat the display name for existing users. Read the following articles for details:
- How to change display names of Active Directory users (support.microsoft.com)
- Change the display names of Active Directory users with Active Directory Services Interface script (support.microsoft.com)
- Use PowerShell to Modify Existing User Accounts in Active Directory (blogs.technet.com – Hey, Scripting Guy! Blog)
- Default full name format in Active Directory (serverfault.com)
Hopefully these articles provide the details you need to make a domain-wide display name change within your Exchange organization. Remember that it is a two-step process: first change the default user-Display createDialog for new users, then update each existing user in the domain to match the new display name format (one-by-one or with a script similar to examples in above linked articles).