Does this work offline? Fastmail’s first party iOS app has such an amazing lack of offline functionality that I’m seriously considering canceling my Fastmail subscription. (Also the lack of threading is getting old.)
I was a Fastmail customer for many years but moved to apple’s iCloud+ when they introduced custom domain support as that works entirely offline on all my devices. Also that gives iPhone/mac integrated contacts and calendars with zero hassle that actually syncs to everything properly. It’s cheaper per seat as well (£25 a month for that plus Apple Music for 6 people a month). No brainer.
It doesn't provide full offline support by keeping a complete cached copy of all mail data on disk, as an IMAP client might. Any content received from the server will remain accessible offline and during subsequent app launches.