Microsoft Exchange Server

Microsoft Exchange Server is a mail server and calendaring server developed by Microsoft. It runs exclusively on Windows Server operating systems.

The first version was called Exchange Server 4.0, to position it as the successor to the related Microsoft Mail 3.5. Exchange initially used the X.400 directory service but switched to Active Directory later. Until version 5.0, it came bundled with an email client called Microsoft Exchange Client. This was discontinued in favor of Microsoft Outlook.

Exchange Server primarily uses a proprietary protocol called MAPI to talk to email clients, but subsequently added support for POP3, IMAP, and EAS. The standard SMTP protocol is used to communicate to other Internet mail servers.

Exchange Server is licensed both as on-premises software and software as a service (SaaS). In the on-premises form, customers purchase client access licenses (CALs); as SaaS, Microsoft charges a monthly service fee instead.

History

Microsoft had sold a number of simpler email products before, but the first release of Exchange (Exchange Server 4.0 in March 1996) was an entirely new X.400-based client–server groupware system with a single database store, which also supported X.500 directory services. The directory used by Exchange Server eventually became Microsoft's Active Directory service, an LDAP-compliant directory service which was integrated into Windows 2000 as the foundation of Windows Server domains.

As of 2020, there have been ten releases.

Current version

The current version, Exchange Server 2019, was released in October 2018. Unlike other Office Server 2019 products such as SharePoint and Skype for Business, Exchange Server 2019 could only be deployed on Windows Server 2019 when it was released. Since Cumulative Update 2022 H1 Exchange 2019 has been supported on Windows Server 2022. One of the key features of the new release is that Exchange Server can be deployed onto Windows Server Core for the first time. Additionally, Microsoft has retired the Unified Messaging feature of Exchange, meaning that Skype for Business on-premises customers will have to use alternative solutions for voicemail, such as Azure cloud voicemail. Unified Messaging continues to exist in Exchange Online requiring an Exchange Plan 2 license.

New features

*Security: support for installing Exchange Server 2019 onto Windows Server Core
*Performance: supports running Exchange Server with up to 48 processor cores and 256 GB of RAM

Removed features

*Unified Messaging

Clustering and high availability

Exchange Server Enterprise Edition supports clustering of up to 4 nodes when using Windows 2000 Server, and up to 8 nodes with Windows Server 2003. Exchange Server 2003 also introduced active-active clustering, but for two-node clusters only. In this setup, both servers in the cluster are allowed to be active simultaneously. This is opposed to Exchange's more common active-passive mode in which the failover servers in any cluster node cannot be used at all while their corresponding home servers are active. They must wait, inactive, for the home servers in the node to fail. Subsequent performance issues with active-active mode have led Microsoft to recommend that it should no longer be used. In fact, support for active-active mode clustering has been discontinued with Exchange Server 2007.

Exchange's clustering (active-active or active-passive mode) has been criticized because of its requirement for servers in the cluster nodes to share the same data. The clustering in Exchange Server provides redundancy for Exchange Server as an ''application'', but not for Exchange ''data''. In this scenario, the data can be regarded as a single point of failure, despite Microsoft's description of this set-up as a "Shared Nothing" model. This void has however been filled by ISVs and storage manufacturers, through "site resilience" solutions, such as geo-clustering and asynchronous data replication. Exchange Server 2007 introduces new cluster terminology and configurations that address the shortcomings of the previous "shared data model".

Exchange Server 2007 provides built-in support for asynchronous replication modeled on SQL Server's " Log shipping" in CCR (Cluster Continuous Replication) clusters, which are built on MSCS MNS (Microsoft Cluster Service—Majority Node Set) clusters, which do not require shared storage. This type of cluster can be inexpensive and deployed in one, or "stretched" across two data centers for protection against site-wide failures such as natural disasters. The limitation of CCR clusters is the ability to have only two nodes and the third node known as "voter node" or file share witness that prevents "spit in the brain" scenarios, generally hosted as a file share on a Hub Transport Server. The second type of cluster is the traditional clustering that was available in previous versions, and is now being referred to as SCC (Single Copy Cluster). In Exchange Server 2007 deployment of both CCR and SCC clusters has been simplified and improved; the entire cluster install process takes place during Exchange Server installation. LCR or Local Continuous Replication has been referred to as the "poor man's cluster". It is designed to allow for data replication to an alternative drive attached to the same system and is intended to provide protection against local storage failures. It does not protect against the case where the server itself fails.

In November 2007, Microsoft released SP1 for Exchange Server 2007. This service pack includes an additional high-availability feature called SCR (Standby Continuous Replication). Unlike CCR, which requires that both servers belong to a Windows cluster typically residing in the same datacenter, SCR can replicate data to a non-clustered server, located in a separate datacenter.

With Exchange Server 2010, Microsoft introduced the concept of the Database Availability Group (DAG). A DAG contains Mailbox servers that become members of the DAG. Once a Mailbox server is a member of a DAG, the Mailbox Databases on that server can be copied to other members of the DAG. When a Mailbox server is added to a DAG, the Failover Clustering Windows role is installed on the server and all required clustering resources are created.

Licensing

Like Windows Server products, Exchange Server requires client access licenses, which are different from Windows CALs. Corporate license agreements, such as the Enterprise Agreement, or EA, include Exchange Server CALs. It also comes as part of the Core CAL. Just like Windows Server and other server products from Microsoft, there is the choice to use User CALs or Device CALs. Device CALs are assigned to devices (workstation, laptop or PDA), which may be used by one or more users. User CALs, are assigned to users, allowing them to access Exchange from any device. User and Device CALs have the same price, however, they cannot be used interchangeably.

For service providers looking to host Microsoft Exchange, there is a Service Provider License Agreement (SPLA) available whereby Microsoft receives a monthly service fee instead of traditional CALs. Two types of Exchange CAL are available: Exchange CAL Standard and Exchange CAL Enterprise. The Enterprise CAL is an add-on license to the Standard CAL.

Clients

Microsoft Exchange Server uses a proprietary

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