RPC over HTTP Protocol Specifics


This topic provides details about the HTTP protocol and the RPC protocol. Both sections include information about the Microsoft® Exchange Server service ports.

HTTP Protocol

HTTP Feature Details


HTTP with SSL: 443

HTTP: 80

The HTTP session should always be established over Secure Sockets Layer (SSL) (port 443). If you offload SSL, you have to configure the AllowAnonymous registry entry to tell the RPC over HTTP Proxy networking component to accept non-SSL connections. For more information about how to configure the RPC proxy server for SSL offloading, see How to Configure the RPC Proxy Server to Allow for SSL Offloading on a Separate Server.




The HTTP protocol uses these two new HTTP verbs to establish the HTTP tunnel to the RPC proxy server.

Content Length

1 GB

1 GB of RPC request data can pass through the tunnel before Microsoft Office Outlook® must reset the tunnel.

Minimum Connection Time-out

30 seconds

The connection time-out on the Web site that hosts the RPC over HTTP proxy networking component cannot be less than 30 seconds. If the connection time-out is less than 30 seconds, the RPC over HTTP proxy networking component will not load.


Microsoft RPC allows communication and the exchange of data between processes. Outlook uses RPC to exchange data with the Exchange store and with Active Directory® directory service.

RPC Information Details

Protocol Sequence


A protocol sequence is the language that a network operating system uses to talk over the network to other computers. The protocol sequence is a string that represents a combination of an RPC protocol, a transport protocol, and a network protocol. NCACN refers to the Network Computing Architecture connection-oriented protocol. Ncacn_http is a connection-oriented TCP/IP sequence that uses Internet Information Services (IIS) as an HTTP proxy. For more information about Microsoft RPC Protocol Sequences, see Selecting a Protocol Sequence (https://go.microsoft.com/fwlink/?LinkId=45960).

When Outlook does not connect to Exchange Server by using RPC over HTTP, it uses ncacn_ip_tcp. Ncacn_ip_tcp is a connection-oriented TCP/IP sequence.

In Exchange Server 2003 SP1, the referral service of DSProxy distinguishes an RPC over HTTP session from an RPC over TCP session by using the protocol sequence.


Microsoft Exchange Information Store service: 6001

referral service of DSProxy: 6002

proxy service of DSProxy: 6004

Active Directory (if the global catalog server and Exchange Server are on the same server): 6004


The system attendant does not load the DSProxy component on a server that is both a global catalog server and an Exchange server.

After the RPC proxy server removes the RPC requests from the HTTP session, it forwards the requests over TCP to services listening on these ports.


The Exchange Server and directory services Universal Unique Identifiers (UUIDs):

Microsoft Exchange Information Store: a4f1db00-ca47-1067-b31f-00dd010662da

System Attendant directory referral: 1544f5e0-613c-11d1-93df-00c04fd7bd09

System Attendant directory proxy: f5cc5a18-4264-101a-8c59-08002b2f8426

Active Directory: f5cc5a18-4264-101a-8c59-08002b2f8426