Send & Receive Issues

How to Fix Outlook Mailbox Full Error When Storage Is Available

Phi Hung Vo Oct 22, 2026 868 views

Question details

The user is unable to receive new emails or send Teams attachments because Outlook reports the mailbox is full, despite local settings indicating available space.

How to Fix Outlook Mailbox Full Error When Storage Is Available

Product: Outlook Professional Plus 2021
Device & OS: not provided
Scenario: Receiving new incoming emails and sending documents via Microsoft Teams.
Observed behavior: Outlook displays a 'mailbox full' error and blocks new messages and attachments, even though the local mailbox storage appears to have considerable free space.

Before you start

Log in to Outlook on the web to verify your overall Microsoft account storage limits, as shared cloud storage capacity often causes discrepancies with local email storage.

Solution 1Recommended

Clear Shared Microsoft Cloud Storage (OneDrive)

Microsoft accounts share storage across Outlook, OneDrive, and Teams. If your connected OneDrive is full, it will block Outlook from receiving new emails.

Recent updates to Microsoft storage policies mean that email attachments and Teams data count toward your general Microsoft cloud storage quota. Even if your email inbox has space, a full OneDrive will trigger a mailbox full error.

Access Outlook Web Settings

Navigate to Storage Settings

Go to 'General' in the left sidebar, then click on 'Storage' to view the breakdown of your Microsoft cloud storage usage.

Identify Full Storage Locations

Check the usage bars for both 'Microsoft storage' (OneDrive/Teams) and 'Email storage'. Identify which quota has reached its maximum limit.

Free Up Space

Click 'Free up space' next to the corresponding category. Delete unnecessary large files in OneDrive or empty the Deleted Items folder in Outlook to restore functionality.

Account Quota Limit: You cannot bypass this by creating a new, separate OneDrive account. Your email is intrinsically tied to the specific Microsoft account and its associated storage limit.

Solution 2

Repair Corrupted Outlook Data Files

A corrupted local PST or OST data file can cause Outlook to falsely report that the mailbox is full and block synchronization.

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Frequently Asked Questions

Why is my Outlook mailbox full when I have space left?

Microsoft recently updated its storage policy so that Outlook attachments now count against your OneDrive cloud storage quota. If your OneDrive is full, Outlook will block incoming emails even if the email mailbox itself technically has space remaining.

Can I create a new OneDrive account to fix the Outlook email block?

No, your Outlook email is permanently tied to a specific Microsoft account and its associated OneDrive storage limit. You must free up space on the currently connected account or purchase a higher storage tier to resume receiving emails.

How do I clear space in Outlook without deleting important emails?

You can archive older emails locally to a PST file, empty your 'Deleted Items' and 'Junk Email' folders, or sort your inbox by size and save large attachments to your local hard drive before removing them from the server.

Outlook & Email Problems