Oh my god Frickin' preach. I've halfway debated vibe coding one because I am so sick of a terrible mail clients and calendars for Linux. Endeavour is pretty decent, but again, it's calendar interface and to-do interface kind of suck.

you wouldn't believe how many obvious things don't exist

Doesnt roundcube support webdav? That's my webmail solution.

I loved Gmail's desktop UI and features.... never will find another like it.

You can use Sogo It reads external caldav but you need to use their caldav instance for writes