@Ctek
As promised I have started a howto. The dokuwiki syntax is hating me 
Perhaps you can help me?
Something is going crazy at the following lines.
vi /etc/e-smith/templates-custom/postfix/postmap/40smarthosts-accounts
If you change the "-" to an "_" from 40smarthosts-accounts all further formatting is lost.
Some lines before is nearly exactly the same text without any problems.
Why?
Here is the link http://wiki.nethserver.org/doku.php?id=howto:how_to_configure_nethserver_for_mail_configuration_with_office365_multiple_mailaccounts