On the Inbound tab of SMTP properties, there is a box for port 25, and alternate, which is usually 587.
If you are relaying mail through your ISP, most of them require authentication (which means, passing your Username and Password with any message you send out. If you are using an email client such as Microsoft Outlook, in the Tools->Accounts tab, under Servers tab, enter your account username and password for your ISP account.
If you are creating emails via a script, you need to write code that includes the Username and Password. I finally solved this after 4 months.