The issue is caused by Microsoft storage being over quota, not just the Outlook.com mailbox itself. Outlook.com email and Microsoft cloud (OneDrive + unified storage) are related but have separate limits, and exceeding either can stop email.
Key points from the behavior described:
- One place shows about 5.7/5 GB used: this is the Microsoft cloud storage quota (OneDrive/unified storage, 5 GB for free accounts).
- Another place shows 5.7/100 GB: this is the Outlook.com email storage (with a Microsoft 365 subscription, mailbox can be up to 100 GB).
- If the Microsoft unified storage is full, Outlook.com cannot send or receive mail even if the mailbox shows plenty of space.
To restore email flow, storage must be brought back under the unified/cloud quota, not just the mailbox quota.
Follow these steps:
- Check unified/cloud storage status
- In Outlook.com, open Settings and search for Storage.
- If there is a message like “Microsoft Unified Storage is full” or similar, the cloud storage (OneDrive/unified) is over quota, which blocks email.
- Free up Microsoft cloud storage (OneDrive/unified)
When unified storage is exceeded:
- Outlook.com cannot send or receive email, even if email storage is below its limit.
- OneDrive files become read-only and new files cannot be uploaded.
To get back under quota:
- Delete or move files from OneDrive (especially large files, photos, videos, or old backups).
- Empty OneDrive recycle bin after deleting files so the space is actually freed.
- If Outlook.com attachments are stored in cloud storage, deleting large emails with big attachments can also help.
If already a Microsoft 365 subscriber and the mailbox shows 100 GB but unified storage still shows 5 GB, the subscription may not increase the unified storage beyond the free tier in the way expected. In that case, the only supported options are:
- Continue freeing up space until total usage is below the 5 GB unified quota, or
- Use the provided option to buy a subscription or free up storage space via the storage management links shown in the storage page.
- Confirm email storage is under quota
- In Outlook.com Settings > Storage, review the breakdown of folders.
- Use the Clean up Mailbox options to permanently delete items (or items older than 3, 6, or 12 months) in large folders such as Deleted Items, Junk Email, and Sent Items.
- Wait and test
- After getting both unified/cloud storage and email storage under their quotas, wait a short while and then send a test message to the account from another email address.
- Any messages that bounced while storage was full cannot be recovered; senders must resend them once storage is back under the limit.
If the storage page still shows conflicting values after cleanup, verify that the correct Microsoft account is being checked (some users have multiple accounts or old profiles where the over-quota usage resides) and ensure the cleanup is done on the account that shows the 5.7/5 GB usage.
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