Oh I’m sorry outlook is one of the few providers that don’t work.
See Provider Overview and https://github.com/deltachat/deltachat-core/issues/561
Outlook seems to have an header white list that removes all email headers that are not on it. And the delta chat headers aren’t on their white list yet.
I recommend using a different email provider, check the Provider Overview to see which ones are known to work with deltachat.