So, I made a fresh, official installation of nextcloud 17.0.3 via snap, then opened an http port, ran installation wizard, enabled https and voila. It’s working.
But as soon as I made a new user, I received an email from a third-party provider, telling me that my account has been created, and for all other similar matters, like changing passwords etc. I allowed for the possibility that my installation got hacked, and re-installed the service, only to face the same confusion. This only happens when https is enabled. I checked the logs, and nothing at all important comes up.
Is this my security issue or a nextcloud installation feature? Any advice would be warmly appreciated.