Not sure; probably something in a .plist you can set via policy. You may want to try asking in the #outlook2016-for-mac or #microsoft-office or $office-365 channels on the MacAdmins Slack (https://macadmins.slack.com). There are several MS people (many of them product managers or development managers) that hang out there and will help with questions. I've got good feedback on OneDrive, MAU, etc.
I did post the question in the #outlook2016-for-mac channel, I'll let you know if someone responds.
I asked concurrently here and in the #microsoft-office Slack channel, and @pbowden was able to resolve it there. I also removed exactly what it was from my original post here, because it sounds like it was not yet meant for public eyes.
Thanks!