Hi Nick

We recently acquired some IP space, but it seems outlook does not want to receive email from that space.

If there's someone that knows what we need to do, we would be grateful for any pointers in the right direction.

First sign up for snds and get the ips under your control. This will allow you to see what state they are in https://sendersupport.olc.protection.outlook.com/snds/ Note that MS throttles all new IPs until they get a baseline on what the IP is sending, so if you have mail servers with new IPs they will take time to get up to speed. So if you have a lot of 451 errors from them this may be the cause. Then you can try and open a ticket. https://support.microsoft.com/en-us/supportrequestform/d75c9d92-a918-3a46-52... They will tell you to sign up for sender support, follow there guidelines for sending etc. But I have had some success with them, not always , but there are not really any alternatives that I know if. Brian