The default port is 25 if your mail server uses this port you just put in your email server address. You need to talk with your web hosting provider to verify the name of your smtp mail server if you are unsure. In the host area - after you set up your smtp server info - you need to hit the Test link to verify that everything is working ... if all is correct you will receive an email to the email address listed in the Host Email: field in the top section of the Host Settings page.