[2-3-7-43-1807]

i love fastmail web ux but i hate that the fastmail app is useless without internet. no browsing of cached mails.

[emestifs]

Use something like imail, thunderbird, etc? Those should all work offline for browsing cached content

[ghostpepper]

The biggest issue with apple's Mail.app is they don't support vanity domains the way Fastmail does. You can add them individually but the Fastmail app lets you create one right from within the compose box - you just type whatever you want into the From: field.