A suggestion (to Fastmail): add an indicator to the mail dashboard that warns when there are delivery issues. Currently it just displays as though all is dandy. I was only made aware that I might have undelivered mail because I tried to sign in to a service that emails a login code which never got delivered. It took 20 minutes to trace the problem back to Fastmail. I have to go through a search engine to find the status page. I can easily imagine a more delicate situation where, expecting time sensitive communication from another party, action with non-trivial consequences is subsequently taken based on the belief that it was never sent. Just informing clients that "hey, we have mail that isn't displayed" could go a long way.