Hi Mangooly,
First you need to set upp a connection to Postmark with API-connector. See our settings in attached pictures. There are probably different ways to do this but we just followed the API documentation from Postmark.
You can of course use the plugin from @gf_wolfer but wanted to use the template function to be able to send not just plain text. At Postmark you can set up the templates with HTML or CSS. Here you will need som basic HTML och CSS coding skills. Sendgrid has an editor which makes this step easier but at the end of the day I think I prefer to have control of every single line of code.
One you set up the connection and built some templates you can start sending mails. You can create static or dynamic templates at Postmark. If you are sending a static onboarding mail to all your customers your can set this up at Postmark. If you need to change the mail content in the future you need to change the code at Postmark. You can also set up dynamic templates to be able to send variables in the mail like order number, price etc.
For implementation you just change the workflow steps. One you set up the api-connection you will find the Postmark steps under Plugins. So if you are using the built in send mail workflow step today just insert the new Postmark step after the old one and just copy the settings. Test it and once it is working you can delete to old workflow step.
Twilio acquired Sendgrid 2018 so i think it is more or less the same company.
Good luck!!
