Registering for a murena account fails with "This email address is disposable" even though it is not

I wanted to create an Issue in the according murena issue board but could not find one.

When Signing up for a new murena account to connect to my freshly installed smartphone, I wanted to use a private mail address I created on my personal mail server for that special purpose. I do not use throw-away-mailboxes, but the login screen falsely detects my mail address as "disposable". See attached screenshot.

Are there any plans to support custom mail providers?

PS: The web Installer worked exceptionally well!