Mail exchange record
Provide a mail exchange record pointing to
mx1.hdm-stuttgart.de. Test this configuration using
dig accordingly.
Caveat: Configuring a client machine using your name server and
sending a mail to xy123@g7.sdi.mi.hdm-stuttgart.de won't
actually work since mail.hdm-stuttgart.de will reject mails
being sent to any domain other than certain subdomain of
hdm-stuttgart.de.
