MAPI over HTTP in Exchange Server

Messaging Application Programming Interface (MAPI) over HTTP is a transport protocol that improves the reliability and stability of the Outlook and Exchange connections by moving the transport layer to the industry-standard HTTP model. This allows a higher level of visibility of transport errors and enhanced recoverability. Additional functionality includes support for an explicit pause-and-resume function. This enables supported clients to change networks or resume from hibernation while maintaining the same server context.

Implementing MAPI over HTTP does not mean that it is the only protocol that can be used for Outlook to access Exchange. Outlook clients that are not MAPI over HTTP capable can still use Outlook Anywhere (RPC over HTTP) to access Exchange through a MAPI-enabled Client Access server.

In Exchange 2016 and Exchange 2019, MAPI over HTTP can be applied across your entire organization, or at the individual mailbox level.

Benefits of MAPI over HTTP

MAPI over HTTP offers the following benefits to the clients that support it:

  • Enables future innovation in authentication by using an HTTP based protocol.

  • Provides faster reconnection times after a communications break because only TCP connections—not RPC connections—need to be rebuilt. Examples of a communication break include:

    • Device hibernation

    • Changing from a wired network to a wireless or cellular network

  • Offers a session context that is not dependent on the connection. The server maintains the session context for a configurable period of time—even if the user changes networks.

MAPI over HTTP when upgrading Exchange

In Exchange 2016 or later, MAPI over HTTP is enabled by default at the organization level, although you still need to configure the virtual directories as described in Configure MAPI over HTTP for users to take advantage of it.

The scenarios where MAPI over HTTP is enabled or disabled by default at the organization level are described in the following table:

Exchange 2019 Exchange 2016
Upgrading from an Exchange 2016 environment MAPI over HTTP is enabled by default n/a
Upgrading from an environment that contains any Exchange 2013 servers MAPI over HTTP is disabled by default MAPI over HTTP is disabled by default
Upgrading from an Exchange 2010 environment n/a MAPI over HTTP is enabled by default

During the upgrade from an organization that contains Exchange 2013 servers, administrators will receive the MAPI over HTTP isn't enabled [WarnMapiHttpNotEnabled] readiness check warning, and enabling MAPI over HTTP post-installation is recommended. In any organization that contains Exchange 2013 servers, MAPI over HTTP won't be enabled by default, and administrators will need to follow the steps in Configure MAPI over HTTP to enable it.

Supportability and Prerequisites

Consider the following requirements to enable MAPI over HTTP.

Supportability

Use the following matrix to verify that your clients and servers support MAPI over HTTP.

Product Exchange 2019 Exchange 2016 Exchange 2013 SP1 Exchange 2013 RTM Exchange 2010 SP3
Outlook 2013 SP1 and all later versions of Outlook MAPI over HTTP
Outlook Anywhere
MAPI over HTTP
Outlook Anywhere
MAPI over HTTP
Outlook Anywhere
Outlook Anywhere RPC
Outlook Anywhere
Outlook 2010 SP2 with updates
KB2956191 and KB2965295 (April 14, 2015)
MAPI over HTTP
Outlook Anywhere
MAPI over HTTP
Outlook Anywhere
MAPI over HTTP
Outlook Anywhere
Outlook Anywhere RPC
Outlook Anywhere
Outlook 2013 RTM Outlook Anywhere Outlook Anywhere Outlook Anywhere Outlook Anywhere RPC
Outlook Anywhere
All earlier versions of Outlook Outlook Anywhere Outlook Anywhere Outlook Anywhere Outlook Anywhere RPC
Outlook Anywhere

Prerequisites

The following conditions are required for clients and servers to support MAPI over HTTP with Exchange Server. Once the following prerequisites are in place, see Configure MAPI over HTTP to enable it in your organization.

  • Supported Outlook clients (see the table in the previous section).

  • .NET Framework 4.5.2 or later. Note that this is no longer an issue for Exchange 2016 CU5 or later. For more information about the .NET Framework requirements for Exchange 2016, see .NET Framework.