Teams Webinar on E3 W/O Exchange Online Plan

Hi @Carson535, 

Thank you for reaching out to the Microsoft Q&A Forum and for clearly outlining your concern. 

Based on the details you shared, you want to host and schedule a Teams Webinar using an E3 account that does not have an Exchange Online mailbox, and you are seeing a calendar error in both the Teams desktop client and Teams on the web. I truly appreciate the clear explanation of your two tenant setup and the time you took to capture and share the error details, as it helps me narrow down the root cause efficiently. 

The issue arises because Teams calendar and webinar features depend on an Exchange Online mailbox to manage meeting data effectively. Specifically, when users sign in with an E3 license lacking Exchange Online, Teams encounters the "OwaUserHasNoMailboxAndNoLicensesAssignedError," preventing calendar access. Consequently, hosting webinars directly requires either an Exchange Online mailbox or a properly configured hybrid Exchange setup. 

To assist you further, please follow each outlined step by step for straightforward implementation: 

1/ Assign Exchange Online to webinar hosts 

• In the Microsoft 365 admin center, assign an Exchange Online plan (for example, Exchange Online Plan 2 or the full E3 including Exchange) to the specific users who need to schedule and host Teams webinars. 
• After the license change, allow time for the mailbox to provision, then ask the user to sign out of Teams, clear the Teams client cache, and sign back in to refresh the calendar. 

2/ Use the tenant where the Exchange mailbox exists 

• If users already have mailboxes in a separate Exchange Online tenant, consider hosting webinars from that tenant/account where the mailbox resides, so Teams can use the existing Exchange mailbox for calendar and webinar data. 
• Make sure those accounts have the appropriate Teams and webinar permissions and policies enabled (for example, “Allow webinars” in Teams meeting policies).  

3/ Configure or verify Exchange hybrid for on‑premises mailboxes (if applicable) 

• If the mailboxes are on‑premises Exchange, ensure a supported hybrid configuration with OAuth is in place so Teams can read and write calendar data to those mailboxes.  
• Verify that Autodiscover and EWS are published correctly and that the required service principal endpoints are configured, then test Teams–Exchange connectivity using the available diagnostic tools. 

4/ Use an account with a mailbox as the webinar organizer while keeping attendees on E3 without Exchange 

• As an interim workaround, designate a set of organizer accounts that have Exchange Online mailboxes and use those accounts to create and manage Teams webinars, while your E3‑without‑Exchange users join as presenters or attendees. 
• This allows the organization to run webinars without changing licensing for every user, focusing Exchange Online licenses only on the users who actually need to create and manage the events. 

5/ Contact IT administrator: 

Since your account is managed by your organization, please contact your IT administrator to review your permissions and policies. If the issue persists after these checks, ask your IT administrator to submit a support request directly to Microsoft Support team.      

They can raise a support ticket by visiting: Get support - Microsoft 365 admin | Microsoft Learn 

If the error remains after completing the steps above, please reply with your Windows version, and a screenshot of the full error window. With those details, I can provide the most targeted next action for your environment. 

As community moderators, we appreciate your understanding that our access to internal development details is limited. Our primary role is to guide users toward the appropriate resources and support channels. While we may not have visibility into deeper backend analysis, we’ll continue doing our best to support you within the scope of our responsibilities.    

I hope this information is helpful. Please follow these steps and let me know if it works for you. If you have any updates regarding the issue, please feel free to share them with me.      

Thank you for your patience and your understanding. I look forward to continuing the conversation. 

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