Outlook emails stuck in the Outbox: how to fix it

Applies to: classic Outlook for Windows (Microsoft 365, 2024, 2021, 2019 and 2016) and the new Outlook for Windows. Outlook on the web and Outlook.com are covered where the steps overlap.

A stuck message is a sending problem. If mail isn’t arriving in your inbox, that’s a separate job; see Outlook not receiving emails.

Classic or new Outlook?

The fixes depend on which app you use, so check first. Classic Outlook has a File tab and a Send / Receive tab on the ribbon. The new Outlook for Windows looks much like Outlook on the web and has no Send / Receive tab.

Fix	Classic Outlook	New Outlook for Windows
Go back online	Turn off Work Offline, then Send All	Check the internet connection
Large attachment	Go offline, move the message to Drafts, remove the file	Open the Outbox message and remove the file
Changed password	Enter it when Outlook prompts, or update the account	Select the account name, then Continue
Mail waits for F9	Turn on Send immediately when connected	Not applicable
Add-ins	Start in safe mode	No safe mode; remove add-ins you added

1. Make sure Outlook is online

Mail queues in the Outbox whenever Outlook thinks it has no connection, and it stays there until the connection comes back. Microsoft notes that pressing Send while you’re disconnected is a common way for messages to end up stuck.

Classic Outlook: open the Send / Receive tab and look at Work Offline. If the button is highlighted, Outlook is offline. Select it once to reconnect, then select Send All. The status bar at the bottom of the window should stop saying Working Offline or Disconnected.

New Outlook: there’s no Work Offline button to check, so start with the connection itself. Open a browser and load a site such as bing.com. If nothing loads, fix the network first; Outlook will send once it reconnects. Microsoft’s can’t send or receive troubleshooter also suggests a manual sync with Sync on the View tab, though that button isn’t offered for Gmail, Yahoo, iCloud or other POP and IMAP accounts.

A VPN that dropped, a hotel or airport Wi-Fi sign-in page, or a laptop that just woke from sleep can all leave Outlook briefly offline. If messages leave the Outbox as soon as you reconnect, nothing else needs fixing.

2. Remove a large attachment

If one message stays in the Outbox while others go out, its size is the most likely cause, and Microsoft’s Outbox page names a large attachment as the usual reason. Mail servers cap message size, and a message over the limit is retried again and again. Microsoft’s troubleshooter adds that one oversized message can hold up the messages queued behind it, and suggests starting with the oldest message in the Outbox.

The limit depends on your provider, and Microsoft’s pages don’t give a single figure for every account. Its send troubleshooter uses 20 MB as the point to remove an attachment, and its Outlook.com page uses 25 MB. Keep in mind that attaching a file makes it larger in transit, so a file just under the limit can still be too big once it’s sent.

In classic Outlook

1. On the Send / Receive tab, select Work Offline so Outlook stops trying to send.
2. Open the Outbox folder in the folder pane.
3. Either delete the message, or drag it to Drafts, open it there and remove the attachment.
4. If Outlook says it’s still sending the message and won’t let you move it, close Outlook. If it doesn’t close, press Ctrl + Shift + Esc to open Task Manager, end Microsoft Outlook (outlook.exe) on the Processes tab, then open Outlook and repeat steps 2 and 3.
5. Select Work Offline again to go back online.

In new Outlook

Open the Outbox folder, open the stuck message, remove the large file and send again. If you can’t edit it, copy the text into a new message and delete the stuck one.

Instead of attaching a big file, upload it to OneDrive or another cloud service and send a link. Microsoft recommends this for files over the size limit, and the recipient gets the current version rather than a copy.

3. Mail only sends when you press F9

If messages sit in the classic Outlook Outbox until you press F9 or select Send / Receive All Folders, automatic sending is switched off. Go to File > Options > Advanced, and under Send and receive turn on Send immediately when connected, then select OK.

If that option is grayed out, your organization controls it through Group Policy, so only your IT department can change it. New Outlook doesn’t have this setting.

4. Don’t open messages inside the Outbox

Classic Outlook usually shows a message waiting to be sent in italics. If you open a queued message from the Outbox and close it again, Outlook may stop treating it as ready to send, and the italics disappear. Open it once more and select Send to queue it again. If you need to change a queued message, go offline first and move it to Drafts rather than editing it inside the Outbox.

5. Update a changed password

If you recently changed your email password, or your provider forced a change, Outlook can’t sign in to send, and mail piles up in the Outbox. Microsoft’s troubleshooter covers this for new Outlook: select the account name, choose Continue when the sign-in window opens and enter the new password.

If Outlook asks you to create an app password, sign in to your email provider’s website, generate an app password there and paste it into Outlook instead of your normal one. Some providers require this when two-step verification is on.

In classic Outlook, you usually get a password prompt; enter the new password and choose to remember it. If Outlook prompts again and again, follow Outlook keeps asking for password.

6. Check that your mailbox isn’t full

A full mailbox can block sending as well as receiving. Microsoft says plainly that if your Microsoft cloud storage is full, you can’t send or receive email. On personal accounts that storage is generally shared with OneDrive, so a full OneDrive may stop your mail too.

Sign in to Outlook on the web to see how much space you’re using. Emptying Deleted Items and Junk Email and deleting old messages with large attachments are the quickest ways to free space. Work accounts have their own mailbox quota set by your organization.

7. Rule out add-ins with safe mode

Add-ins that scan or change outgoing mail, such as antivirus, signature and CRM tools, can hold messages in the classic Outlook Outbox. Safe mode starts Outlook without add-ins, which shows quickly whether one of them is involved.

1. Close Outlook.
2. Hold Ctrl and open Outlook from its shortcut, then select Yes when asked about safe mode. Alternatively, press Win + R, type the command below and select OK.
3. Send a test message. If it leaves the Outbox, an add-in is the likely cause.
4. Go to File > Options > Add-ins, choose COM Add-ins next to Manage, select Go, and clear the add-ins one at a time, restarting Outlook normally between tries.

outlook /safe

Microsoft documents these steps on its safe mode page for classic Outlook. New Outlook doesn’t have the same safe mode; if you’ve added add-ins there, removing them from the account is the closest equivalent.

If Outlook shows an error

Sometimes Outlook tells you why the message is stuck. Read the error in the Send / Receive progress window in classic Outlook, or the banner in new Outlook, before changing anything.

• A 5.7.57 or “client not authenticated” error means the server refused the sign-in for sending, often after a password change or because SMTP authentication is turned off for the mailbox. See 530 5.7.57 Client not authenticated.
• A message size error confirms the attachment problem in Fix 2.
• Errors that mention the server, port or encryption on IMAP or POP accounts point to the outgoing server settings. Compare them with the settings your provider publishes, since they differ between providers.

Last resorts: repair or a new profile

If none of the fixes above work and messages are stuck for every recipient, the problem may be in Outlook’s installation or profile rather than in the messages.

• Repair Office: a Quick Repair fixes damaged program files without touching your mail. Our Office repair guide covers Quick Repair and Online Repair.
• Reset Outlook: in classic Outlook, a new mail profile rebuilds the account settings; in new Outlook, you can reset the app from Windows settings. Both are covered in how to reset Outlook to default settings. Note any custom settings first, because a reset removes them.

For work or school accounts on Microsoft 365, also check whether colleagues have the same problem. If several people can’t send at once, the cause is likely on the server side, and your IT department or the Microsoft 365 service health page is the place to look.

Related guides

• Outlook not receiving emails: how to fix it
• Outlook keeps asking for password: how to stop it
• 530 5.7.57 Client not authenticated to send mail: how to fix it
• How to reset Outlook to default settings (classic and new Outlook)
• How to repair Microsoft Office (Quick Repair and Online Repair)

Official sources

• Microsoft Support: Fix messages that are stuck in the Outbox
• Microsoft Support: I can’t send or receive messages in Outlook
• Microsoft Support: Outlook email stuck