Wrong sender for Thunderbird appointments in connection with a Nextcloud


I have Nethserver 7.9 in connection with a Nextcloud and Thunderbird.

The Nethserver is included in the Active Directory, and the Nextcloud is therefore also a member of the AD.

When I plan appointments in Thunderbird, the fully qualified AD user name is always used instead of the email address.

I have already entered the actual email address everywhere in Nextcloud and Thunderbird.

I have changed everything I could find accordingly.

How can I make it so that an email address is used as the sender (e.g. name@gmx.net), and NOT the AD user name “user@domain.local”?

Thanks and best regards,