We need a mailing tool to send highly individual mails to customers, triggered via an api. The mails should have a content like "It's been a while, here is what you missed:", followed by stuff that is individual to each recipient. Along with the usual options to unsubscribe from these mails, etc.
If you know trello, you know what I mean, they send mails like these to notify you of new activities that you are tagged in etc.
Can you recommend a service that allows for this?