In HUIT's O365 tenant we have set up "stub" accounts in Office 365 so that HBS email and contact information is visible in our Global Adress list. In addition, HBS has their own separate Office365 tenant. Because of these factors, there is some nuance in order fore HBS users to use a SharePoint site.
O365 Groups and Teams require HBS users to log into HUIT's O365 tenant using thier NetID@harvard.edu. To share with HBS users you have to enter their name as you would any user at Harvard and they will show up in the people picker. HBS users who do not know their NetID may call the HUIT Service Desk at 617-495-7777. (For more information on NetID please see: https://reference.iam.harvard.edu/faq/what-my-netid-and-why-it-important.
NOTE: HBS users will need to use their NetID@harvard.edu as user name and HarvardKey password to access any document, SharePoint, or site in HUIT's Office 365 tenant.