[gus_massa]

I was going to recommend one of the patio11 posts, but I'm not sure which one. IIRC in one of them he recommend to give some small free advice in each post to convince people to buy your product. (I hope I'm not misremembering too much.)

His own selection of his best posts https://www.kalzumeus.com/greatest-hits/

I can't find the best one, but this may be helpful. https://training.kalzumeus.com/lifecycle-emails

Take a look at https://training.kalzumeus.com/ and see how he get's your email.