Hello, thank you for reaching out to Microsoft Q&A.
With a Personal Microsoft account (without an Office 365 subscription), you get 5 GB of OneDrive cloud storage and 15 GB of Outlook.com email storage.
If you exceed either of these limits, you will not be able to send or receive emails.
To free up space in your account, open an InPrivate/Incognito browser window and sign in with your Microsoft account here:
https://outlook.live.com/mail/0/options/accounts-category/storage
Select Free up space under either OneDrive or Outlook (Attachments), depending on which one is using more of your storage.
Delete emails with large attachments and/or large files stored in OneDrive.
Make sure you back up any important files before deleting them from OneDrive.
Alternatively, you can increase your storage quota by purchasing an Office 365/Microsoft 365 subscription here:
https://www.microsoft.com/en-us/microsoft-365/onedrive/onedrive-plans-and-pricing