TLDR: You can’t test the SMTP email feature of a Unifi Cloud Key from the cloud. You have to connect to the controller directly.
Longer version:
I recently upgraded my wi-fi to a Ubiquiti Unifi system including the Unifi Cloud Key which allows me to connect to, manage, and report on my network via a hybrid cloud service. Everything has been working a treat…except for email notifications. The Unifi Cloud Key acts as a controller and part of its configuration allows you to setup a connection to an email server so that events / alerts can be raised and delivered via email. I had setup a specific mailbox on my O365 account for this and after confirming that it was able to send mail, I entered its credentials into the Controller and hit the “Send test email” button…which resulted in an error. Hmm. I scratched my head, double checked my settings and tried it again. Still failed. What’s going on? I checked my O365 account. Everything is fine there. Tried telnet to smtp.office365.com on port 587…yeah,server is there. Tried another app to test credentials and that was OK. Finally I gave in, wised up and pinged Ubiquiti support in a live chat (oh, didn’t I mention that the Unifi controller supports live chat with support? It does!). The Ubiquiti rep had me connect to the controller directly rather than to the Unifi Cloud Service and test it there et voila! Works like a charm. So the net is that to test the controllers email functionality you have to connect to it directly rather than over the cloud service. Lesson learned and I hope this helps someone else out there.