There are two ways to send emails using our platform: API, or SMTP. The difference between the two is that when a campaign is sent out through API it comes with an Opt-Out button (which can be disabled), and what happens after you press ‘Send’ on your email will vary based on how the bounce rate has been set up in response rules; while if sending via SMTP there’s no way for someone to opt out of receiving future mailings from Transactional Email - but bounces do not auto end up back at you like they would come with ACTIVE Campaigns and templates built inside our editor.