I've come across the same issue. I am in a support session about it now. I'll try to remember to update this thread when resolved.
Outlook Connector Page not opening
Saichetan
6
Reputation points
Hi All,
When I am trying to develop outlook actionable messages and trying to open below link to register my smtp it is not opening and the below error is coming....Please help.
https://outlook.office.com/connectors/oam/publish