This is an entry in FastMail's series of Advent Calendar blog posts that they do every year. I'm glad to see them continue the tradition this year, and it's valuable to get this level of insight into a company that I trust with my mail. If you're interested in seeing more, check this year's first Advent Calendar post which has links to their calendars from 2014, 2015, and 2016, which are all worth reading if you're a FastMail customer or just interested in how running a mail hosting company works: https://blog.fastmail.com/2017/12/01/fastmail-advent-2017/