Check end of May exactly on status site you have linked. 9 hours of outbound email delivery issues in total and 2 hours of interrupted access to services so yea

Check end of May exactly on status site you have linked. 9 hours of outbound email delivery issues in total and 2 hours of interrupted access to services so yeah, not very cool for your delivery time sensitive business. 100% uptime doesn't exist and Fastmail isn't any better than Proton or Tuta.