I have a couple of smaller personal projects that need transactional emails (mostly just notifications of things that have happened or weekly summaries, etc). Currently using Postmark but now they're going away from credits to monthly subscriptions. I don't send nearly enough emails to justify doing the monthly subscription, but I send more than the free tier allows (this is the case for most services). I'd probably be at the cusp of your free tier but I also have 3 domains. Currently I'm sending approximately 2k emails per month, if you had a hobby plan around $5/mo with unlimited domains and around 5k emails per month - I would sign up. Otherwise I'll probably just load up on Postmark credits and then eventually switch off to something else entirely down the road.