Microsoft Exchange Server 2016 Architecture

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With the release of Exchange Server 2016 Microsoft took the opportunity to simplify some of the architecture complexity that was present in previous versions. It also includes new features which make communication and collaboration easier. Microsoft has changed the way Exchange deployment has been done for the last few releases. Implementation is now easier, the configuration is simpler, and upgrading has fewer steps. The number of servers required have been reduced, as have licensing costs and infrastructure requirements. Hybrid deployments are also much easier using on premise and Exchange Online or Office 365, which can further reduce the required on premise infrastructure.

Microsoft simplified the architecture by removing the Exchange 2013 Client Access Server role and added it as a service on the Exchange 2016 Mailbox Server Role. Now there is just one Exchange 2016 Mailbox Server role with Client Access and Transport services included on it. The Edge Transport Server is retained from the previous versions of Exchange and provides inbound and outbound mail routing as well as anti-spam, antivirus, and content connection filtering via address rewriting to protect internal servers.

The new Microsoft Exchange Server 2016 Building Block Architecture is presented in Figure 1. The Exchange Server 2016 mailbox servers on the Internal network are the points of communication for all clients, Active Directory and all other services that communicate with Exchange server. Internet client communication is also routed to the Exchange mailbox server. It is not recommended you expose the Exchange Client Access server directly on the Internet. Traffic should be routed via a LoadMaster appliance acting as a reverse proxy. The Edge Transport server should also be positioned in the perimeter network where it can help protect the internal mailbox servers. DNS MX records should be configured to use the Edge Transport server, or to any hosted solution like Microsoft Online protection which can then forward mail to the Edge Transport server.


Figure 1: Microsoft Exchange Server 2016 Building Block Architecture

The Microsoft Exchange Server 2016 Client Access Service (CAS) running on the mailbox servers can communicate with legacy Exchange servers using the same protocols as Exchange Server 2013 and 2010. This includes protocols like EWS, MRS Proxy, and SMTP Transport. If Exchange 2016 sends an email to a Exchange 2013 user, then the Exchange 2016 transport service forwards the email to an Exchange 2013 server and then the mail is delivered to the user’s mailbox. This feature helps Exchange Server 2016 to co-exist with legacy Exchange servers without having to implement a completely new Exchange Server 2016 deployment. Currently Exchange Server 2016 can co-exist only with Exchange Server 2010 SP3 RU11 and Exchange Server 2013 CU11. It cannot co-exist with Exchange 2007 or earlier versions.


Figure 2: Exchange 2016 Server Communication with other Exchange versions

In Exchange Server 2016 clients connect to a mailbox server, but the interactions are with the Client Access Service that is running there. The target mailbox that a client is using could be on the same server or a different mailbox server. In the latter case the Client Access Service proxies the client connection to the correct backend server connected to the active Exchange database.


Figure 3. Clients Communication with Exchange 2016 Mailbox Server

Below are some noteworthy new features and improvements in Exchange Server 2016.

Mailbox Server Enhancement Features

  1. Database Divergence Detection – Detects database corruption, determines the cause, then fixes the issue and reseeds the failed database to return it to a healthy state.
  2. Loose Truncation – Introduced initially in Exchange Server 2013 SP1. If a server or database is offline, then the other active and passive copies accumulate all the transaction logs without truncation until the offline server/database comes online. This can lead to the available disk space on these servers filling up and cause them to go offline. Loose Truncation allows each database copy to track its own free disk space and start to truncate transaction log files independently if the available disk space falls below a threshold set by the administrator.
  3. ReFS Support – Resilient File System (ReFS) is a new file system introduced in Windows Server 2012. Exchange Server 2013 databases could be placed on this file system. In Exchange Server 2016 it is recommended. It provides more robust storage and resilience features to reduce the possibility of database corruption, and hence the number of database reseeds.
  4. Replay Lag Manager – Introduced as part of the high availability enhancements in Exchange 2013. It is a component of the Microsoft Exchange DAG management service, the process that deals with tasks like checking whether databases have sufficient redundancy.
  5. DAG deployments are simpler and can be deployed without a cluster administrative access point
  6. DAG File Share Witness instances can now be placed in Microsoft Azure to provide 3rd party site resilience
  7. Content or search indexes are built from the local database copy rather than from the active database, which can sometimes cross the network, thus reducing network utilization.
  8. BitLocker can be used to encrypt Exchange Server 2016 disks to provide additional security.
  9. OPs use has been reduced by 22% from Exchange 2013 which allows more users per mailbox server.

Hybrid Enhancement Features

  1. Exchange Server 2016 is Cloud ready and built on hybrid capabilities introduced in Exchange Server 2013 and tested in Exchange Online and Office 365 over the last few years.
  2. Exchange Server 2016 on premise deployments also make use of some of the Office 365 Cloud features such as archiving, data loss prevention, rights management, advanced thread protection, mobile device management, and SPAM & virus filtering.

Client Enhancement Features

  1. MAPI over HTTP is now the default protocol for Outlook communications with Exchange Server. MAPI over HTTP is a more robust, stable and reliable client communications protocol.
  2. Outlook and Outlook Web Access (OWA) can collaborate with SharePoint Server 2016 or OneDrive for Business to share and edit documents with email recipients. Email recipients are automatically provided permissions to edit shared documents.
  3. Search has been significantly enhanced in Exchange Server 2016. Search speed is also greatly increased, and Calendar items can also be searched via OWA.
  4. A smarter Inbox in Outlook 2016 helps users to manage email to increase their efficiency and productivity. It also includes a new intelligent recipient and people search, a ‘Tell me what you want to do’ search option, plus the ability to do inline previews of URLs and videos in Outlook 2016.
  5. Enhancements in OWA include one-click archiving, better spell checking and autocorrect, contacts import from CSV files, better format controls, better attachment views, inline replies, insert images, pin items, undo, and more.

Mobile Enhancement Features

  1. Mobile Outlook increases productivity by providing a rich user experience on phones and tablets. It now presents two tabs called Focused and Other. Outlook intelligently uses Focused for all important email, and Other contains items like newsletters, system notifications, subscriptions and another general email. Search in Mobile client is improved to provide filtered and accurate search results.
  2. One of the new interesting features in mobile Outlook is Send Availability. It is used to send available time slots to recipients when planning meetings.
  3. Mobile Calendar view has been improved. It provides more detailed information of all invitees and other meeting information. It also allows joining a Skype meeting directly from a mobile device.

Security and Compliance Enhancement

  1. The Data Loss Prevention (DLP) feature has been enhanced by adding new DLP sensitive information types into Exchange.
  2. Auditing has been enhanced and updated with a new architecture and schema. Built on the Exchange 2013 Audit log model, it follows the Office 365 Audit logging schema. In Exchange Server 2016 audit logs are no longer stored in a user’s mailbox, but rather in a centralized audit report mailbox for the organization. This helps with the long term retention of logs and the generation of reports from the log data.
  3. eDiscovery search has been improved via the eDiscovery console to provide more reliable results and increased speed. Public Folders can now also be put on hold so that contents cannot be deleted.