Hello Natalie Spencer, welcome to Microsoft Q&A forum.
The "0 bytes over 5GB storage" warning is about your cloud storage limit (OneDrive + email attachments). To fix it, you can try to free up some space:
- Sign into Outlook.com > Settings > General > Storage to see what's using space
- Delete emails with large attachments, then empty your Deleted Items folder
- Check OneDrive for large, unnecessary files
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