Read the section on "slots". They keep two copies in New Jersey, and one in Seattle.
However, based on the post mortem, it sounds like they're not willing to invoke failover at the drop of a hat. They allude to needing complex routing to keep their old good-reputation IP addresses alive. That might have something to do with it. (They were "only" 3-5% down during the outage, which is bad for them, but not unusual by industry standards.)
https://www.fastmail.help/hc/en-us/articles/1500000278242
Read the section on "slots". They keep two copies in New Jersey, and one in Seattle.
However, based on the post mortem, it sounds like they're not willing to invoke failover at the drop of a hat. They allude to needing complex routing to keep their old good-reputation IP addresses alive. That might have something to do with it. (They were "only" 3-5% down during the outage, which is bad for them, but not unusual by industry standards.)