Outlook Memory Full Issue – Unable to Send/Receive Emails

Dinesh Kumar Mathiyarasan 40 Reputation points
2026-09-01T11:57:58.4066667+00:00

Outlook Memory Full Issue – Unable to Send/Receive Emails

I’m facing an issue with Outlook where I’m getting a message that the mailbox/memory is full. Because of this, I’m unable to send or receive emails properly.

I have already checked and deleted some unnecessary emails and attachments, but the issue still occurs. I would like to understand how to identify whether this is related to the Outlook mailbox quota, OST/PST file size, or the system’s RAM usage.

What are the recommended troubleshooting steps to identify the exact cause and resolve this issue without losing any emails?

Outlook | Windows | Classic Outlook for Windows | For business
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Answer accepted by question author
Helen Luu 2,785 Reputation points Independent Advisor
2026-09-01T13:24:09.4466667+00:00

Hello @Dinesh Kumar Mathiyarasan

I understand that you are experiencing an issue where you are unable to send or receive emails because your Outlook mailbox is full.

This issue commonly occurs when your mailbox has reached its storage limit. To review your mailbox storage and quota, you can go to Settings > Account > Storage or refer to the following Microsoft Support article: Mailbox storage limits in Outlook | Microsoft Support

Please note that when you delete emails or other mailbox items, they are moved to the Deleted Items folder and will continue to count toward your mailbox storage quota. To free up space, please ensure that you also permanently remove items from the Deleted Items folder. Once the cleanup is completed, it may take up to 24 hours for the updated storage usage to synchronize and reflect accurately.

You can also consider moving older emails to your Online Archive mailbox. This can help free up space in your primary mailbox while allowing you to retain access to older messages. After sufficient space has been freed, you should be able to send and receive emails normally.

For more information about Online Archive mailboxes, please review: Manage email storage with In-Place/Online Archive mailboxes | Microsoft Support

Additionally, if you are licensed with Exchange Online Plan 1, your subscription will includes 50 GB of mailbox storage and 50 GB of archive mailbox storage. For additional storage, you can request your IT admin an upgrade to Exchange Online Plan 2, which provides 100 GB of mailbox storage and 100 GB of archive mailbox storage. Furthermore, when the archive mailbox reaches approximately 90% of its quota, auto-expanding archiving can be enabled. This feature allows archive storage to grow automatically and can provide up to 1.5 TB of storage capacity.

For more details, please refer to: Learn about auto-expanding archiving | Microsoft Learn

Please let me know if you need any assistance reviewing your mailbox usage or managing your mailbox storage.

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  1. AI answer

    2026-09-01T11:58:34.8733333+00:00

    Use this sequence to isolate the cause without deleting mail permanently.

    1. Check whether the mailbox quota is the actual blocker
    • In Outlook, go to File > Tools > Mailbox Cleanup.
    • Use View Mailbox Size to see total mailbox size and which folders are largest.
    • Check Deleted Items specifically. That folder still counts against the mailbox quota until it is emptied.
    • Use Find items older than or Find items larger than to locate mail that can be moved or removed.
    • Search for large messages with: messagesize:>5 mb
    • If using the new Outlook or Outlook on the web with a work or school account, mailbox usage can also be checked in Settings > Accounts > Storage.

    What this confirms:

    • If the mailbox is near or over quota, sending and receiving can stop until space is freed.
    1. Determine whether the local OST/PST file is too large
    • Large .ost or .pst files can cause Outlook pauses and errors even after mailbox cleanup.
    • Outlook guidance for .ost files:
      • Up to 5 GB: generally good experience
      • 5–10 GB: performance depends on hardware
      • More than 10 GB: short pauses begin on most hardware
      • 25 GB or larger: pauses become more frequent
    • In Outlook 2010 and later, the maximum .pst size is 50 GB.
    • The default maximum size for a Unicode .pst or .ost file is approximately 25 GB.

    What this confirms:

    • If mailbox size is reasonable but Outlook is still slow, freezing, or showing memory-related behavior, the local data file size is a likely factor.
    1. Reduce the mailbox safely before removing anything important
    • Empty Deleted Items.
    • Check for redundant messages in long threads and use Conversation Clean Up if appropriate.
    • Move older items to an archive .pst if archiving is available in the organization.
    • Save large attachments outside the mailbox, such as to OneDrive or a local folder, then remove them from messages if no longer needed in-mailbox.

    Low-risk approach to avoid data loss:

    • Prefer moving mail to an archive .pst instead of deleting it.
    • If deleting, verify whether items are going to Deleted Items and empty that folder only after confirming nothing is needed.
    1. Compact the Outlook data file after cleanup Deleting items does not automatically shrink a .pst or .ost file.
    • Manually compact the data file after cleanup.
    • This is the supported way to reduce the actual file size after mail has been removed.

    What this confirms:

    • If space was freed in Outlook but the file size did not drop, compaction is required.
    1. If the error specifically says there is not enough free memory This can also be caused by Outlook configuration rather than system RAM alone.
    • If a large .pst is open, close the .pst file or reduce the number of folders in it.
    • Disable or uninstall Outlook add-ins to test whether they are contributing to the issue.

    What this confirms:

    • A “not enough free memory” message in Outlook can be triggered by a large .pst or too many enabled add-ins, not only by physical RAM pressure.
    1. If mail still will not send or receive after cleanup Check common send/receive blockers:
    • Confirm internet connectivity.
    • Check the Outbox for a stuck message with a large attachment.
    • If an attachment is larger than 20 MB, remove it and resend with a smaller file or a link instead.
    • If the account password changed recently, update it in Outlook.
    • Antivirus email scanning can also interfere with send/receive.

    Practical interpretation for the three causes:

    • Mailbox quota issue: mailbox size is high, Deleted Items is large, and send/receive stops until server storage is reduced.
    • OST/PST size issue: Outlook is slow, pauses, or shows memory-like errors even after mailbox cleanup; local file remains large until compacted.
    • System RAM/add-in issue: Outlook shows “not enough free memory,” especially with large PSTs or many add-ins enabled.

    Recommended order:

    1. Run Mailbox Cleanup.
    2. Empty Deleted Items and find large/old mail.
    3. Archive or move mail before deleting if retention is needed.
    4. Compact the data file.
    5. If the error persists, test with add-ins disabled and reduce open PST usage.
    6. Check Outbox and large attachments if send/receive is still failing.
    AI-generated content may be incorrect. Read our transparency notes for more information.

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