FWIW, I can't connect via my home or office fiber (separate providers), but on my T-Mobile 5G it works fine. When I do a traceroute it gets stuck in Cloudflare's network. I'm in Europe.

EDIT: I did some more testing from some other machines around the world. Most are able to connect, some aren't. When I compare the traceroutes it looks like a networking issue on Fastmail's end. They look mostly identical except for the last hop. That's also what their status page says[1].

[1] https://fastmailstatus.com/clji5sqvg99220wtohhj3e2d2b

Web app and IMAP/POP mail access affected. I've been with them for years and this is the first outage I've experienced. Feeling for the people tripping over themselves on a Friday afternoon to fix this!