Wow, that's a surprise! I love Postmark and I am using it for all my products. This kind of feels wrong though, hopefully it won't go downhill from here.
https://smtp2go.com maybe? Just discovered them the other day but yet to give it a whirl. Just when I was starting to double down on Postmark, they did this. Not blaming them, but we all know this is going to go badly (as a previous Active Campaign user).