What are the best transactional email service providers?

Hey there, this question has already been asked (and answered) on the site:

https://www.slant.co/topics/136/~best-transactional-email-services

Hey, I thought this could be separated into a Con and a Pro, hope you don't mind!

Hey! Hope you don't mind, I reworded your first person phrasing. Does it sound ok? We prefer second or third which makes it friendlier for others to edit.

Hey Jason, thanks for the contribution! Could you please explain in more detail how exactly MJML makes using the email service easier? What are some of the main features?