Unable to receive or send emails throughout the day

The error message "UserHasNoMailboxAndNoLicenseAssignedError" typically indicates that the affected account does not have a mailbox or an appropriate license assigned:

Please try the following

Step 1: Verify License Assignment

1. Log in to the Microsoft 365 Admin Center.
2. Navigate to Users > Active Users.
3. Select the affected user and check if they have an Exchange Online license assigned. If not, assign the appropriate license.

Step 2: Confirm Mailbox Creation

1. After assigning the license, ensure that the mailbox has been provisioned.
2. You can check this by navigating to Exchange Admin Center > Recipients > Mailboxes and searching for the user.

Step 3: Reassign Licenses (if necessary)

If the mailbox still doesn't appear, try removing the license, waiting for a few minutes, and then reassigning it. This can trigger mailbox creation.

Step 4: Check for Sync Issues

If the user is part of a hybrid environment, ensure that their on-premises mailbox is properly synced with Exchange Online. Use the Azure AD Connect tool to verify synchronization.

Step 5: Clear Browser Cache

Sometimes, browser cache issues can cause login problems. Clear the cache and cookies of the browser and try logging in again.

Step 6: Use PowerShell for Advanced Troubleshooting

Connect-MsolService
Get-MsolUser -UserPrincipalName <UserEmail> | Select-Object DisplayName, Licenses