I have found a fix for this issue.
I have installed Invoiceninja with the email handler on “log”. When the installation progress is done, i have changed it back to “smtp”.
To fix the SSL / TLS error, i used this solution from engrkashi:
stream_socket_enable_crypto(): SSL operation failed with code 1 Laravel 7 (laracasts.com)
I don’t know if this is the safest solution, but it worked for me