no way to integrate with cloudron mail like the Rainloop app in Nextcloud.
On that specific point, Nextcloud Mail does fine in my experience if the users have their cloudron email as their primary email, then you can do similar to the following (my.demo.com used in place of mail server name):
So it can depend a lot on your setup, but I'll freely give you that no sieve support is incredibly frustrating, plus I constantly can't find features that I feel like should be there, and even when it's "working" the visual design is so weird to me that things still feel wrong. I mean, I'd give it like a 4/10 and "would not recommend to a friend" but for some users/clients...it's evidently good enough?
The rolling average in my experience is definitely hot garbage, but sometimes it's acceptable garbage.