Skype for Business currently has open federation. There is no need for me to go into the admin portal and add a domain in order to communicate with them. This makes it very convenient on the IT staff so we aren't constantly working tickets to add a domain to the whitelist. Why is Teams requiring us to add domains and not give us the option to have "open" federation? I moved my team to "teamsonly" mode and quickly found out that I had to add a bunch of external domains that we talk to on a day to day basis.