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 remote procedure call (RPC) protocol called
MAPI/RPC, Exchange Web Services (EWS), an alternative to the MAPI protocol, is a documented
SOAP-based protocol introduced with Exchange Server 2007. Exchange Web Services is used by the latest version of
Microsoft Entourage for Mac and Microsoft Outlook for Mac - since the release of
Mac OS X Snow Leopard Mac computers running OS X include some support for this technology via Apple's Mail application. E-mail hosted on an Exchange Server can also be accessed using
POP3, and
IMAP4 protocols, using clients such as
Windows Live Mail,
Mozilla Thunderbird, and
Lotus Notes. These protocols must be enabled on the server. Exchange Server mailboxes can also be accessed through a web browser, using
Outlook Web App (OWA). Exchange Server 2003 also featured a version of OWA for
mobile devices, called Outlook Mobile Access (OMA). Microsoft Exchange Server up to version 5.0 came bundled with Microsoft Exchange Client as the email client. After version 5.0, this was replaced by Microsoft Outlook, bundled as part of
Microsoft Office 97 and later. When Outlook 97 was released, Exchange Client 5.0 was still in development and to be later released as part of Exchange Server 5.0, primarily because Outlook was only available for Windows. Later, in Exchange Server 5.5, Exchange Client was removed and Outlook was made the only Exchange client. As part of Exchange Server 5.5, Outlook was released for other platforms. The original
Windows 95 "Inbox" client also used MAPI and was called "Microsoft Exchange". A stripped-down version of the Exchange Client that does not have support for Exchange Server was released as
Windows Messaging to avoid confusion; it was included with
Windows 95 OSR2,
Windows 98, and
Windows NT 4. It was discontinued because of the move to email standards such as SMTP, IMAP, and POP3, all of which
Outlook Express supports better than Windows Messaging.
Exchange ActiveSync Support for
Exchange ActiveSync (EAS) was added to Microsoft Exchange Server 2003. It allows a compliant device such as a
Windows Mobile device or
smartphone to securely synchronize mail, contacts and other data directly with an Exchange server and has become a popular mobile access standard for businesses due to support from companies like
Nokia and
Apple Inc. as well as its device security and compliance features. Support for
push email was added to it with Exchange Server 2003 Service Pack 2 and is supported by Windows Phone 7, the
iPhone and
Android phones, but notably not for
Apple's native
Mail app on
macOS. Exchange ActiveSync Policies allow administrators to control which devices can connect to the organization, remotely deactivate features, and remotely wipe lost or stolen devices. ==Hosted Exchange as a service==