Problem: Had a DNAT setup in Astaro to reroute the external IP (DNS resolution) of my OWA server to it’s internal address. However, it would time out every time. Port 80 and other traffic worked fine, it seemed to be only an issue with https (443).
Solution: Had to do a full NAT for this and made the internal address of the Astaro box the new source. After that adjustment, all was well.