ok so,
i'm using the dutch version, i'll try to translate to the correct english menu items
in Setings (Instellingen)
you need to enable developer mode (Activeer de ontwikkelaarsmodus)
then a new menu appears on top : Technical (Technisch)
there you have a selection for E-mail : e-mails -> all mails that are send, outgoing mailserver, incoming mailserver, so the incoming mailserver was not setup...
When doing that, i'll also saw that the outgoing mails were not transmitted, so when looking in the reason why, i saw it tried to send trough the addres notifications@mydomain.be, while the from address was somethingelse@mydomain.be, so in Office365 i've created a new shared mailbox, and now i can send mails...
tickets still not coming in though
When i go to technical/E-mail/Aliasses i see my mailalias from the helpdeskteam, but it has a status untested...
searching now how to 'test'/enable it...

edit 2:fixed!!
i was using a shared mailbox to get my tickets in.
But that mailbox isn't read!
In technical/E-mail/Incoming mailserver, i've put the username as a user that could read this and other shared mailboxes. But Odoo only reads the usernames inbox, so i needed to put in the mailadres from the shared mailbox as username, and now tickets are coming in!