Delist Portal not working

Greetings,

I'm trying to delist my server's IP address using https://sender.office.com/, but all I get is the following error when I try to submit the form:

Step 1: Our messaging service has experienced a temporary issue, please resubmit your information below.

https://i.imgur.com/OQfKDzu.png

I've been trying to resubmit, but it never works. Don't know where to issue a bug report.

Best regards,

Douglas