OL2000: Outlook Cannot Pass SMTP Traffic Over Any Port But the Default (25) When You Use a Secure Connection

If you select the This server requires a secure connection check box, and then change the port to something other than port 25, you cannot connect to Microsoft Exchange Server or any other e-mail server that requires a STARTTLS negotiation.

There are two different methods to obtain a secure connection for Simple Mail Transfer Protocol (SMTP). The first one works as follows:

1. A normal SMTP negotiation takes place.
2. The client issues a STARTTLS command.
3. This starts a Transport Layer Security (TLS) handshake as described in request for comments (RFC) 2246 and RFC 2487.

Outlook 2000 supports this method on the default port of 25, but not on any other port.

The second method is to use a secure socket from the very beginning. Outlook 2000 supports this method on ports other than the default port of 25.

To resolve this behavior, upgrade to Microsoft Outlook 2002; it supports STARTTLS negotiation on ports other than 25.

This behavior is by design.