Front-End and Back-End
Front-end server will not host mailbox and public folder.
You can disable some services in front-end server.
The Exchange Information Store service supports data storage (mailbox and public folder). Since all mailboxes and public folders are hosted in the back-end servers, you can disable this service.
Microsoft Exchange MTA Stacks service supports message routing to foreign messaging system using X.400 and gateway connectors. It is not a required service on a front-end OWA server.
If you do not want the clients access their email by POP3, you can disable POP3.
