- Mailbox servers contain the transport services that are used to route mail.
- Mailbox servers contain mailbox databases that process, render, and store data.
- Mailbox servers contain the client access services that accept client connections for all protocols.
- Clients don’t connect directly to the backend services as explained later in this article.
- Mailbox servers contain the Unified Messaging (UM) services that provide voice mail and other telephony features to mailboxes.
- Exchange admin center (EAC) and the Exchange Management Shell can be used to manage Exchange mailbox servers.
Mailbox high availability:
- A database availability group (DAG) is the fundamental element of the high availability and site resilience framework built into Exchange 2016.
- A DAG is a group of Mailbox servers that host a set of databases and provides automatic, database-level recovery from different types of failures.
- And DAG’s in Exchange 2016 have been improved compared to Exchange 2013.
Transport high availability:
- The Transport service as feature known as shadow redundancy which makes redundant copies of all messages in transit.
- The transport service also makes redundant copies of all delivered messages using feature called Safety Net.
- In Exchange 2016, a DAG represents a transport high availability boundary. You can achieve site resilience by spanning a DAG across multiple Active Directory sites.
Client access protocol architecture:
- The client access services on Exchange 2016 Mailbox servers accepts all forms of client connections.
- The client access (i.e. Frontend) services proxy these connections to the backend services on the destination Mailbox server where user’s mailbox is located.
- Clients don’t directly connect to the backend services.
- Communications are shown in the following diagram.
Edge Transport servers:
- Edge Transport servers handle all external mail flow for the Exchange organization.
- Edge Transport servers are installed in the perimeter network, and are subscribed to the internal Exchange organization with the help of edge-sync process.
- The Edge-Sync process makes recipient and other configuration information available to the Edge Transport server.
- Edge Transport servers provide anti-spam and mail flow rules. Exchange Management Shell is used to manage the Edge transport server.
For comparison between Exchange 2013 and Exchange 2016, do check my other post at below link.