I think 10000 was probably too generous, but 625 also seems a bit too little as well for hobbyists.
Re: Tell HN: Mailgun lowers free-tier API from 10k to 625 emails per month
#11Hobbyist to me means that you are doing it for fun and aren't engaging more than 5-10 people. So given that, I'm having a hard time understanding how 10 people could handle 625 emails a month.