Site Connector and Message Transfer Agent (MTA)
communication within sites both use RPCs to connect, authenticate, and transfer
e-mail messages. Microsoft does not recommend that you use RPCs over a VPN.
RPC communication requires a minimum bandwidth of 56 Kbps and does
not tolerate latency on the network. As a general guideline, a Site Connector
requires at least 56 Kbps of network bandwidth that is available exclusively
for Exchange Server communications. It must be heavily stressed that the
56-Kbps transfer rate is a bare minimum for light mail flow with little or no
directory replication traffic. A VPN cannot provide guaranteed end-to-end
bandwidth over a public network, such as the Internet. Although a VPN
connection can be managed over a public network or over the Internet, the
bandwidth is limited to what is currently available over the current router
path. Periodically, latency can be expected on the network.
Note Site Connectors in a VPN over a public network are
not supported. The options that are supported in a VPN over a public network
are:
- An X.400 Connector if you are running Exchange Server
Enterprise Edition
- The Internet Mail Service with connected sites
Spanning an Exchange Server site across a VPN is also not
supported. A supported configuration is to install or reinstall separate
Exchange sites that are separated by a VPN. To maintain connectivity and
reliable mail flow, Microsoft strongly recommends that you use an X.400
Connector if you are running Exchange Server Enterprise Edition or the Internet
Mail Service if you are running Exchange Server Standard Edition with connected
sites over a VPN.
If a Site Connector uses a VPN connection, you may
have slow or intermittent mail flow, or it may stop mail flow completely. Event
ID 9318, 9316, or 9322 messages may be logged by the Exchange Message Transfer
Agent service in the Application event log. These event ID messages are also
logged if the Site Connector or the MTA communication within sites spans a VPN.
These event ID messages may contain the following error codes :
- 1722: This error code indicates that a connection to the
RPC server cannot be made.This may also indicate a possible name resolution
problem. Verify your name resolution as a best effort approach to resolve this
error.
- 1753: This error code indicates that the Endpoint mapper on
port 135 is not responding to a port request.
- 5: This error indicates that access was denied. To resolve
this issue, use the Override tabs on the Site Connector to
verify the account and password.