Microsoft Outlook won't send email to my email address

Hello,

I'm not an Outlook user, but I received a report that Outlook is having problems sending to my email address. The email address IS valid and working for me, tested by sending from GMail. The address looks like:

alan@cxxxxxm.cloud

My suspicion is that it's not handling the 'cloud' part correctly

The DNS MX records seem to be good.

Without buying (or renting) Outlook, any idea how I can file this as a bug?