Ok, I am not sure if this a just a missunderstanding on my end.
I installed Nethserver 7.5 and enabled AD. Afterwards I installed email module as well as sogo. Now my Domain users have the email.
user@ad.my.tld instead of user@my.tld.
I removed SoGo and installed Webtop 5 - where this “problem” did not occur.
Maybe i did or expect something wrong: What I want is user@my.tld also I want to use SoGo if possible.