Will someone correct or verify my understanding of the following terms:

MAPI (sometimes referred to as TCP)

  1. The on-the-wire RPC protocol format that Outlook uses with Exchange server. The client connects to server ports 135 and 139 (among others) to facilitate communication.

  2. It is a C++ API. The resulting API call sends out a network packet based on the MAPI profile configuration (HTTPS or RPC based)

Image of a TCP/MAPI client connection: Image of a MAPI connected client

RPC over HTTPS (sometimes referred to RPC/HTTPS, RoH, or HTTPS)

  • First introduced with Outlook 2003 and Exchange 2003, RPC/HTTPS tunnels MAPI-based RPC traffic into the HTTP protocol where a CAS server or Front End server proxies the connection to the back end server.

Outlook Anywhere

  • This is the same thing as RPC/HTTPS, with the added logic of using Autodiscover to locate and configure a MAPI-based mail profile. The resulting configuration may use RPC or HTTPs on-the-wire.

Image of a RPC/HTTPS, OutlookAnywhere, or HTTPS client connection enter image description here

  • Seems to be OK for me. MAPI is not only Outlook, but a general "Messaging API", not only used by Outlook
    – MichelZ
    May 29, 2012 at 15:19
  • @MichelZ - I realized that after I posted... refresh and let me know if I made the change you want me to make. May 29, 2012 at 15:20
  • Seems to be OK now, yap
    – MichelZ
    May 29, 2012 at 15:22
  • The base port for RPC is 135, not 139.
    – Massimo
    May 29, 2012 at 16:51
  • @Massimo I wrote 139 twice... was thinking 135. Thanks. May 29, 2012 at 17:06

1 Answer 1


outlook anywhere is RPC over HTTP - it's just a name change. Outlook anywhere's auto configuration is an outlook 2010 ability. Older clients can still use outlook anywhere but must be manually configured. An additional feature (under the outlook anywhere umbrella) is client redirection, which you would set up if you wanted to use SSL or a specific CAS server for a client or group of clients that were not domain joined.

  • 1
    Autodiscover was introduced in Outlook 2007/Exchange 2007.
    – Massimo
    May 29, 2012 at 16:51
  • autodiscover perhaps, but I don't think it had autoconfig (I think you had to use RPC over HTTP without site configs)- I certainly could be wrong
    – Jim B
    May 29, 2012 at 17:12

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