Express Invoice uses, by default, port :96 for accessing data files over the internet. You would link your public address using port 96 so that outsiders can access the data from your Express Invoice from your central server. Then you would need to open port :96 on your router for that to happen. The e-mail function works using your e-mail provider. When setting up your e-mail in Express Invoice go to > 'Other' then > 'E-mail Settings'. Under 'E-mail Settings' check 'Use SMTP to send email directly to the mail server' then enter the command for accessing your e-mail server. This is something you can get from your providers web page, or call them. Usually the settings are like these examples: mail.providername.com, smtp.providername.com or smtp.mail.providername.com. Then you enter your e-mail address and the password you use to check your e-mail.