How can i tell it where my imap server is ?

[primski]

I am using Nextcloud integration.

Tries to connect to localhost but it's not there ...

This folder also doesn't exist on my nextcloud server

Configuration file application.ini is found within directory structure of a special kind, like this:
/var/www/rainloop/data/_data_/_default_/configs/application.ini

From here

[cm-schl]

Hi,

this should help you: https://github.com/the-djmaze/snappymail/wiki/Admin-Manual#menu-domains
The documentation of Rainloop does not cover the whole functionality of the fork SnappyMail...