The Debian Edu mainserver provides an email system (SMTP + IMAP) and
allows students and teachers to communicate internally via mail.

When trying to send an email from a Debian Edu network host (!=
tjener) to <user>@intern or <user>@postoffice.intern via the
localhost's exim4 on the networked host those mails get rejected by
tjener's exim4 setup.

Ideally, people can send mails from any host on the Debian Edu network
to the mailboxes on tjener, also when using mailutils on the cmdline
of a networked Debian Edu host.

Mike