Hey Albert Chen that is good and all but still doesn’t solve the bigger issue. It’s been a major pain inviting external people to our tenants for awhile now since so many people have their email addresses somehow hosted in office 365 and they have no admin or know what to do with their tenants or may not even have the option to fix it. One example I can think of is godaddy hosted emails.
I dont know how many times ive Invited someone and they log into their work accounts and can’t join my tenant. They don’t have admins and don’t even know they have office 365 in many instances. This isn’t just a few people either it’s like 20+% of the guest users that get invited to teams.
The fix is always to setup a new outlook.com account which works but then they have another account and email to manage when it would have been nice to just allow them to login with existing Microsoft azure account instead which usually causes frustration for the user.
If your willing to work with me on this I’d gladly do some ground work and reach out and try to get more examples but it’s definitely an issue I would love to get solved so we can use Teams with external partners without so many support issues!
I know many other admins that have also had similar issues as well. But bottom line is there shouldn’t be a restriction by default for anyone in azuread to not be able to join and access other teams unless it’s a tenant with condition access policy or something in place preventing it.