Reassign the affected user’s Microsoft 365 license with Exchange Online enabled immediately, because removing that entitlement disconnects the mailbox and reassigning it within 30 days restores access and makes the mailbox active again.^1^
1. Restore the user’s license
Because the help tools have left Outlook unlicensed, address that before troubleshooting the original billing banner:
- In the Microsoft 365 admin center, go to Users > Active users.
- Select the affected user.
- Open Licenses and Apps.
- Select the appropriate Microsoft 365 product license.
- Expand its apps/services and ensure Exchange Online and the Microsoft 365 desktop apps are enabled.
- Select Save changes.
Alternatively, go to Billing > Licenses, select the product, choose Assign licenses, add the user, and select Assign. If assignment fails, open that product’s Errors & Issues tab to identify issues such as no available license, conflicting service plans, or an invalid usage location.^2^
Do not repeatedly remove and re-add the license. Exchange Online data associated with a removed license is retained for 30 days; adding the license back during that period restores mailbox access.^3^
2. Separate mailbox delivery from the Outlook warning
After the license assignment succeeds, open Outlook on the web and check whether new test messages arrive.
- Mail arrives on the web: Exchange Online and the mailbox are functioning; the remaining problem is Classic Outlook activation, authentication, or its local profile.
- Mail does not arrive on the web: Treat this as an Exchange Online mail-delivery problem rather than an Outlook billing-banner problem.^4^
For missing mail:
- In the admin center, open Health > Service health and inspect Exchange Online for an incident.^5^
- Go to Admin > Exchange > Mail flow > Message trace.
- Set a date range covering a known missing message.
- Add its sender and the affected recipient, then select Search.
- Open the result and review Status, Details, and How to fix it:
- Delivered indicates the service delivered it to the mailbox; investigate mailbox rules, filtering, or the Outlook client.
- A failed, blocked, or pending result provides the mail-flow action to take.
- No result suggests the message did not reach your Exchange Online organization or requires investigation from the sender’s side.^4^
3. Clear the desktop activation warning
If Outlook on the web works, close all Microsoft 365 applications, including Outlook, Word, and Excel. Then:
- Open a Microsoft 365 app and sign out of the affected work account.
- Close every Microsoft 365 app.
- Restart Windows.
- Open an app and sign back in with the licensed work account.
- If the banner offers Reactivate, select it and authenticate.
Microsoft documents this process for unexpected product deactivation; licensing-level changes, including removing and re-adding assignments or changing service plans, can trigger deactivation.^6^
If activation still fails, run the Microsoft 365 activation troubleshooter on that same Windows PC. It requires Windows 10 or later. Reinstall Office only if that troubleshooter does not resolve the activation problem.^7^
4. Escalate now if the mailbox remains unavailable
Given the three-day outage, open a Microsoft 365 business support request if the license cannot be assigned, the mailbox remains unavailable after assignment, or message trace shows an unexplained service-side failure:
- In the admin center, select Help & support at the lower right.
- Describe both issues separately: Exchange Online license/mailbox unavailable and incorrect billing/activation banner.
- If suggested results do not help, select Contact Support, choose phone or email, and submit the request.
If all subscriptions were purchased through a Microsoft partner, contact that partner instead.^8^
References
- Can't access the mailbox of an unlicensed user in Exchange Online
- Assign or unassign licenses for users in the Microsoft 365 admin center
- Delete or restore user mailboxes in Exchange Online
- Find and fix email delivery issues as a Microsoft 365 for business admin
- How to check Microsoft 365 service health
- Users might receive a Product Deactivated error in Microsoft 365 Office apps | Microsoft Support
- Office error "Account Notice: We've run into a problem with your Microsoft 365 subscription" | Microsoft Support
- Get support for Microsoft 365 for business