Microsoft Exchange Server is a

mail server Within the Internet email system, a message transfer agent (MTA), mail transfer agent, or mail relay is software that transfers electronic mail messages from one computer to another using the Simple Mail Transfer Protocol. In some contexts, the a ...

and calendaring server developed by

Microsoft Microsoft Corporation is an American multinational corporation and technology company, technology conglomerate headquartered in Redmond, Washington. Founded in 1975, the company became influential in the History of personal computers#The ear ...

. It runs exclusively on

Windows Server Windows Server (formerly Windows NT Server) is a brand name for Server (computing), server-oriented releases of the Windows NT operating system (OS) that have been developed by Microsoft since 1993. The first release under this brand name i ...

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 Active Directory (AD) is a directory service developed by Microsoft for Windows domain networks. Windows Server operating systems include it as a set of processes and services. Originally, only centralized domain management used Active Direct ...

later. Until version 5.0, it came bundled with an email client called Microsoft Exchange Client. This was discontinued in favor of

Microsoft Outlook Microsoft Outlook is a personal information manager software system from Microsoft, available as a part of the Microsoft 365 software suites. Primarily popular as an email client for businesses, Outlook also includes functions such as Calendari ...

. Exchange Server primarily uses a proprietary protocol called

MAPI Messaging Application Programming Interface (MAPI) is an Application programming interface, API for Microsoft Windows which allows programs to become email-aware. While MAPI is designed to be independent of the protocol, it is usually used to com ...

to talk to

email client An email client, email reader or, more formally, message user agent (MUA) or mail user agent is a computer program used to access and manage a user's email. A web application which provides message management, composition, and reception functio ...

s, but subsequently added support for

POP3 In computing, the Post Office Protocol (POP) is an application-layer Internet standard protocol used by e-mail clients to retrieve e-mail from a mail server. Today, POP version 3 (POP3) is the most commonly used version. Together with IMAP, i ...

IMAP In computing, the Internet Message Access Protocol (IMAP) is an Internet standard protocol used by email clients to retrieve email messages from a mail server over a TCP/IP connection. IMAP is defined by . IMAP was designed with the goal of per ...

, and EAS. The standard

SMTP The Simple Mail Transfer Protocol (SMTP) is an Internet standard communication protocol for electronic mail transmission. Mail servers and other message transfer agents use SMTP to send and receive mail messages. User-level email clients typi ...

protocol is used to communicate to other Internet mail servers. Exchange Server is licensed both as

on-premises software On-premises software (abbreviated to on-prem, and often written as "on-premise") is installed and runs on computers on the premises of the person or organization using the software, rather than at a remote facility such as a server farm or clo ...

and

software as a service Software as a service (SaaS ) is a cloud computing service model where the provider offers use of application software to a client and manages all needed physical and software resources. SaaS is usually accessed via a web application. Unlike o ...

(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 April 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

service, an

LDAP The Lightweight Directory Access Protocol (LDAP ) is an open, vendor-neutral, industry standard application protocol for accessing and maintaining distributed Directory service, directory information services over an Internet Protocol (IP) networ ...

-compliant directory service which was integrated into

Windows 2000 Windows 2000 is a major release of the Windows NT operating system developed by Microsoft, targeting the server and business markets. It is the direct successor to Windows NT 4.0, and was Software release life cycle#Release to manufacturing (RT ...

as the foundation of

Windows Server domain A Windows domain is a form of a computer network in which all user accounts, computers, printers and other security principals, are registered with a central database located on one or more clusters of central computers known as domain controlle ...

s. 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.

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 A single point of failure (SPOF) is a part of a system that would Cascading failure, stop the entire system from working if it were to fail. The term single point of failure implies that there is not a backup or redundant option that would enab ...

, 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 Log shipping is the process of automating the backup of transaction log files on a primary (production) database server, and then restoring them onto a standby server. This technique is supported by Microsoft SQL Server, 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 "split 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 {{Short pages monitor * – official site {{Email servers Groupware

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Exchange Server Exchange Server 1996 software Microsoft Office servers