Unlike previous versions of Outlook, Outlook 2016 does not allow manual configuration of server settings, and is instead solely dependent on the autodiscover process. This causes the initial autodiscover process to take 20-30 minutes.

Not only that, it's set to check that every couple of hours instead of just using it for the first-time account. Turns out that, for some reason, Outlook looks for Exchange autoconfigure settings from first and then it looks at. Then our Mac users started getting certificate errors in Outlook.