To be clear, Postfix is the Open Source Linux software for sending email. In a perfect world, Postfix would be all you need for sending. Providers like Postmar

To be clear, Postfix is the Open Source Linux software for sending email. In a perfect world, Postfix would be all you need for sending. Providers like Postmark and Mailgun let you forward and send email through them. Essentially, you are paying these companies to deal with IP address reputation management and ensure high deliverability.