Thanks. The free tier looks good. The only issue I have is I use a different alias for every account so I think I'd run out with only 25.
What the 25 aliases allotted in the free tier allows you to do is have 25 different domains.
Happy to answer any questions that you might need!
Our decision was to not use STARTTLS for port 25, but that's maybe not a good idea and we should allow it back: this would make both services happier ;)
In a nutshell: TLS via 465 works correctly, and STARTTLS via 587 too.
Don't hesitate if you want to weight on this, happy to discuss this further!