Problem with auto-login in nextcloud

[tregmos]

Hello!
I have a problem with the auto-login to snappymail in nextcloud.
I have got two independent nextcloud installations on different webservers with different users. In both of them I have activated the snappyMail app and added e-mail adresses. In one of these installations the snappymail auto-login works perfect. Even when I log out from snappymail inside nextcloud, it immediately logs in again automatically.
But on my other nextclout installation this doesn´t work. I always have to enter my snappymail credentials. I have tried to change my nextcloud user-credentials, so that they are the same like the log-in credentials in snappymail, and I tried every possible settings combination in the snappyMail Webmail settings in the advanced settings of nextcloud, but nothing works. I also compared every single setting in both of my snappymail apps on both nextcloud installations, and they are identical. Even the settings of the webserver domains (php versin 8.1, http>https, etc.) are identical. The settings in both snappyMail admin panels are also identical. But the auto-login feature on one of the installation doesn´t work, while the other works like a charm.
Does anyone have an idea, what could be the problem with the non-working auto-login feature in one of my snappyMail apps?

[tregmos]

I think I found the solution myself! In the snappyMail admin-Panel I changed the default domain to "nextcloud". I think this was the importatnt change. In the additional settings in nextcloud for snappyMail Webmail I had to chose "Attempt to automatically login users with their Nextcloud username and password, or user-defined credentials, if set.", the options "Don´t fully integrate with nextdloud" and "Debug" I left unchecked. The username (=e-mail address) and password for nextcloud are the same like for snappyMail. Now it works like on my other installation: even when I logout from snappymail inside nextcloud, it immediately logs in again automatically. Sending e-mails also works from several adresses I added to the snappyMail app inside nextcloud. Perfect
But one thing is strange: in my other snappyMail nextcloud installation with well-working auto-login I don´t have nextcloud set as default domain, but my default e-mail domain. And in the additional settings for snappyMail Webmail I have chosen "Users will login manually, or define credentials in their personal settings for automatic logins.". Here the auto-login works with these settings. Why?