Azure - External collaboration settings - Members can invite -- Impact on OneDrive sharing

[mrtoad]

I help support multiple Office 365 tenants.  There's a strange OneDrive sharing discrepancy with new guests issue that has recently happened on a tenant I'll call 'Tenant A'.  A similarly configured tenant I'll call 'Tenant B' for comparison reasons.

About 2-3 weeks ago, Tenant A end users could no longer invite brand new guests (that is, not in this tenant's Azure as guests yet) to share their OneDrive files with.  No major sharing / guest invite settings changes were made that I'm aware of.  However, if either the 'Members can invite' was turned on in Azure, or, if the user account was given the guest inviter role, then that account could share OneDrive files/folders with brand new (to the tenant) outside guests. If the external account is invited to the Tenant A and accepts, then user accounts can successfully share their OneDrive files with that external account with that Members can invite setting being on, .

To make this issue more frustrating Tenant B has virtually all the same sharing settings that Tenant A has, and yet user accounts can share their OneDrive files with brand new (to the tenant) guests.  This is despite on Tenant B, the 'Members can invite' is turned off, and the user accounts do not have the guest inviter role.

I realize many of these share settings in this link target more systems that OneDrive -- https://docs.microsoft.com/en-us/microsoft-365/solutions/collaborate-as-team?view=o365-worldwide -- however I've used it as a baseline to compare the sharing settings between the two tenants, and they're virtually identical.  Have also checked other areas such as https://admin.onedrive.com/ , online SharePoint shell Get-SPOTenant | fl , and conditional access policies, but haven't found any major discrepancies between the two tenants. Does anyone have any ideas? If Tenant B enforced the same new guest invite OneDrive share behavior that Tenant A did, this issue would be a little easier to stomach.  Feel like I'm missing something either very obvious or obscure here.

[#2 · Accepted solution]

The difference might stem from the fact that one of the tenants doesnt have the SPO B2B feature turned on. Without it, SPO/ODFB still use their own mechanism for sharing, effectively bypassing (most) B2B controls across M365. Some details on the difference in behavior can be found here: https://docs.microsoft.com/en-us/azure/active-directory/external-identities/o365-external-user

That said, I believe said feature should be rolled out to all tenants now, but perhaps in your case one is in a different "cloud". Otherwise, the "Members can invite" setting should be mandatory afaik. 

[#3]

@Vasil Michev Thank you Vasil, your guidance was spot on! EnableAzureADB2BIntegration was true for tenant A, and false for tenant B, so I'm almost sure that's the explanation.