How licensing works for work and school accounts in the new Outlook for Windows

sgamfd Yes I think you are correct in your hypothesis based on how you explain it. 

Is it because the primary account that they pay for premium under is a gmail address?

Right now the new Outlook only supports connecting to Microsoft accounts created with a Microsoft email address. See the FAQ I copied below, which was part of the blog post above. When the user ads their Gmail.com today to the new Outlook, you are adding that Google account, not the Microsoft Account created with the Gmail address. So our app isn't aware of that license. Yes, this isn't current supported, though we are working on it. You have two options: 

Option 1: Just have them go back to the classic Outlook until we support this config. 

Option 2: Add an Outlook.com alias to the MSA created with a Gmail address, so you can add it to the new Outlook. See below. 

How do I add a Microsoft Account that was created with a non-Microsoft email address to the new Outlook for Windows?

When you create a Microsoft Account, you have the choice of creating an Outlook.com email address (e.g. @outlook.com or @hotmail.com). Or using your existing non-Microsoft email as your username (e.g. Gmail, Yahoo). Currently, the new Outlook for Windows only supports adding Microsoft Accounts with an Outlook.com/Hotmail.com email address. 

If you purchased a Microsoft 365 Personal or Family subscription with a Microsoft Account that was created with a non-Microsoft email address, you will need to add an Outlook.com alias in order to connect it to Outlook. To do so, follow the instructions here: How to add an email address or phone number to your Microsoft account - Microsoft Support.