Is there an advantage to using my own ISP/Internet connection provider for SMTP services?

Yes, typically there is an advantage to using your ISP for outgoing email services. The main advantage is usually speed/efficiency of sending out the email, since you are directly connected to that provider’s network and there is usually no need for password authentication. In order to keep our own SMTP services secure, we must require SMTP authentication by password, and thus some overhead is present. To try using your ISP for outgoing email service, contact them directly for their outgoing/SMTP server settings information.