Hello, thank you for reaching out to Microsoft Q&A.
Storage:
Please note that with a Microsoft account (without an Office 365 subscription), you get 5 GB of OneDrive cloud storage and 15 GB of Outlook email storage.
If you exceed either of these limits, you will not be able to send or receive emails.
For a Google account (without a Google One subscription), you get a total of 15 GB of storage shared across Google Photos, Gmail, Google Drive, and other Google services.
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First, make sure you know which account is having issues. If you use a @gmail.com address as the sign‑in for a Microsoft services such as OneDrive or Outlook, it is treated as a Microsoft account, not a Gmail account.
In this situation, open an incognito/private browsing tab in any web browser and sign in to your Microsoft account at Outlook.com to check how much storage you have used.
Then, in Outlook, go to Settings > Accounts > Storage.
Note: If your storage has exceeded the limit, your account will be put into a frozen state, and you will not be able to send or receive emails. If you later upgrade your storage or free up some space, it usually takes up to 24 hours for the change to be reflected and for email to start working normally again.
Check your account online first, and then check the Outlook app you are signed in to. If the issue is specific to the app, you can sign out and sign back in to resync your emails.
Let me know if you still need more help.