How to Verify an Outbound Port for Mail Delivery Is set to Port 25


Topic Last Modified: 2005-05-05

To control the ports and IP addresses through which Exchange sends outbound mail, you must configure the SMTP virtual server. SMTP connectors configured on the virtual server inherit these settings.

Two of the SMTP virtual server properties relate directly to configuring Exchange to send Internet mail:

  • The outbound TCP port    Make sure that the outbound port is set to port 25 (the default setting). Of the two settings related to sending Internet mail, this is the setting that you must verify. The following procedure describes how to verify that the outbound TCP port is set to 25.

    Changing the default settings on your default SMTP virtual server can cause mail flow problems.
  • The use of an external DNS server   To send Internet mail, the DNS server Exchange uses must be able to resolve external (Internet) names. For detailed instructions, see How to Specify an External DNS Server That Is Used by the SMTP Virtual Server.

  1. In Exchange System Manager, expand Servers, expand <server_name>, expand Protocols, expand SMTP, right-click Default SMTP Virtual Server, and then click Properties.

  2. On the Delivery tab, click Outbound connections.

  3. In the Outbound Connections dialog box, verify that the TCP port is set to 25. See the following figure.

    Outbound Connections dialog box

    Remote servers on the Internet expect your server to use TCP port25. Changing this setting is not recommended because other SMTP servers typically accept connections on port25 only.