I have been trying to get Office 365 calendar integrated but we are seeing issues with O365 auto discovery.
Exchange server outlook.office365.com failed connection test: Autodiscovery failed: The Autodiscover service couldn't be located
Checking from here against the client domain and it passes for Outlook autodiscovery - Microsoft Remote Connectivity Analyzer
Although it does throw some 443 warnings around SSL. We had Microsoft check and confirm everything is good. I have a case open with Spark support but hoping someone else has seen this before?