To specify additional ports requires editing the registy to add the additional ports. After making these registry key changes you will need to restart the SMTP service.

The registry details follow:

For 32bit Windows:
HKEY_LOCAL_MACHINE\SOFTWARE\Mail Enable\Mail Enable\Connectors\SMTP

For 64bit Windows:
HKEY_LOCAL_MACHINE\SOFTWARE\Wow6432Node\Mail Enable\Mail Enable\Connectors\SMTP

Value Name: Additional Ports
Type: REG_SZ (String)
Format: Port1,RequireAuth,SSL,AuthMode;Port2,RequireAuth,SSL,AuthMode

If RequireAuth is 1 then it requires connections to authenticate before sending.
If SSL is 1 then the port has SSL enabled.

AuthMode can be 0, 1 or 2:

Example: 4091,0,0,0;4098,0,0,0
(Above would result in two additional ports without SSL or Auth before send set).

In order to configure your server for PCI compliance, you will need to change the SMTP listening port in the administration program to something other than 25 and enable the Requires SSL option (port 587 is fine, just disable the submission port if doing this). You then need to configure the Windows registry using the information in this article to listen on port 25, but set authentication to 2. Be aware that if you are configuring the server for PCI compliance that you need to have your Outlook users connect over SSL to the submission port.