MAPI over HTTP provides the ability for Messaging API (MAPI) clients and servers to communicate across a HTTP connection without using remote procedure calls (RPCs)

The Problems with RPC

Although RPC delivers significant advantages to application developers, it’s an old mechanism that was originally designed to work across LANs rather than across the Internet. 

This is our case

Outlook 2013 or outlook 2010

Outlook Anywhere: users connect to Microsoft Outlook with Outlook Anywhere. Formerly known as RPC over HTTP

New transition is: MAPI over HTTP


Two modes of communication that Outlook 2013 SP1 can use with Exchange 2013 SP1

On the left, you have the older RPC-style connections 

On the right, you can see how MAPI over HTTP replaces the dependency on RPC by directing the remote operations executed by Outlook across HTTP connections. This is different than RPC over HTTP because the RPCs used to carry MAPI instructions (wrapped in TCP/IP or HTTP packets) are no longer used. Instead, the MAPI instructions are sent directly over an HTTP link, which is what most Internet applications use to convey their data.

Note: MAPI over HTTP isn’t enabled by default. You have to enable it by updating the organization configuration to let mailbox servers know that it’s OK to tell Outlook clients that MAPI over HTTP is available.

We are using RPC over Http

To enable mapi

This is using RPC

This is using Mapi

Note MAPI/HTTP connections are designated in the Protocol column using the string HTTP.


How does MAPI/HTTP work?

Let’s walk through the scenario of an Outlook 2013 SP1 client connecting to Exchange Server 2013 SP1 after MAPI/HTTP has been enabled.

  1. The Outlook client begins with an Autodiscover POST request. In this request Outlook includes a new attribute that advertises the client is MAPI/HTTP capable with the attribute X-MapiHTTPCapability = 1.
  2. The Exchange server sees the request is coming from a MAPI/HTTP capable client and responds with the MAPI/HTTP information including the settings on how to connect to the mailbox using MAPI/HTTP. This assumes the MAPI/HTTP has been configured and enabled on the server.
  3. The Outlook client detects the new connection path and prompts the user to restart Outlook to switch to use the new connection. While the restart is pending Outlook will continue using Outlook Anywhere. We recommend you deploy the latest Office client updates to provide the best user experience. The updates remove the prompt and clients are allowed to make the transition at the next unprompted restart of Outlook.
  4. After the restart, Outlook now uses MAPI/HTTP to communicate with Exchange.



Outlook is using GUID not Server name

Technical issues in exchange 2013 that we must know

Outlook is using GUID not Server name

Outlook clients no longer connect to a server FQDN as they have done in all previous versions of Exchange. Outlook uses Autodiscover to create a new connection point comprised of mailbox GUID, @ symbol, and the domain portion of the user’s primary SMTP address.

Ex: MailboxGuid @ SMTP Domain (DomainName)

This change has helped to get rid of the message “Your administrator has made a change to your mailbox. Please restart

 It is used in conjunction with AutoDiscover to allow seemless moves of servers for future and current (if you’re moving mailboxes and the like)



Outlook 2013 cannot connect to Exchange 2013 using MAPI over HTTP when proxy is enabled

Disable Mapi=1



Consider the following scenario:
You are using Microsoft Outlook 2013 version 15.0.4569.1506 or later.

  • You are connecting to a Microsoft Exchange Server 2013 Service Pack 1 (SP1) mailbox using the MAPI over HTTP protocol.
  • You have a proxy enabled on your Outlook client computer which has your own domain listed as an Exception.

In this scenario, Outlook cannot connect to Exchange. The Status Bar in Outlook displays DISCONNECTED.


Outlook cannot connect to the Exchange Server using the MAPI over HTTP protocol when a proxy is enabled with your own domain as an Exception.


Microsoft is aware of this issue and may produce a solution in an upcoming release or service pack. Future updates about this solution will be posted to this article.

In order to work around the issue, use one of the following options:

  • Remove your own domain name from the Exceptions in the Proxy settings.
    • In Internet Explorer, click ToolsInternet Options.
    • On the Connections tab, click LAN Settings.
    • Click Advanced.
    • In the Exceptions section, remove your domain.
    • Click OK on the three open Windows.
  • Disable MAPI over HTTP.
    • Exit Outlook if it is running.
    • Open Registry Editor.
      • Open the Run box
        • Windows 8
          Press the Windows key + R
        • Windows 7 or Windows Vista
          Click Start, and then click Run.
      • Type Regedit.exe and click OK.
    • Locate and select the following key in the registry.
    • After you select the key that was specified in step 3, click the Edit menu, point to New, then select DWORD Value.
    • Type MapiHttpDisabled as the name of the DWORD Value, and then press Enter.
    • Right-click MapiHttpDisabled, and then click Modify.
    • In the Value data box, type 1, and then click OK.

Note The MapiHttpDisabled registry value is intended for testing purposes only.