Outlook email stuck

Thank you, I'll try your suggestions.

Hi @John Marshall, 

I hope you're having a productive day.  

Based on the details you shared that your sent emails with an attachment in Classic Outlook remain stuck in the Outbox instead of sending. 

This behavior commonly occurs because Classic Outlook processes outgoing messages one at a time in a sequential queue. As a result, when an email carries a large attachment, it can cause a timeout or stall before the message is fully delivered. Additionally, third-party antivirus software often scans outgoing attachments in the background, which may cause further delays or block the sending process entirely. In some cases, Outlook may also have been switched to Work Offline mode without a clear on-screen indicator, which prevents any emails from leaving the Outbox. 

To help get your emails sending again, please follow the three steps below at your own pace. 

1/ Confirm Outlook is online and refresh the send/receive queue 

• In Classic Outlook, select the Send/Receive tab. 
• Make sure Work Offline is not selected (if it is, click it to turn it off). 
• Click Send/Receive All Folders and wait 1–2 minutes. 
• Close Outlook completely, then reopen it and try sending the message again. 
• Reference: Work offline in Outlook - Microsoft Support 

2/ Clear the stuck message safely and resend it cleanly 

• Go to the Outbox folder and open the stuck email. 
• Choose File > Save As to save a copy as an .msg file (backup). 
• Remove the attachment, then click Send (this checks whether the queue clears). 
• Create a new email and reattach the file; if the attachment is large, compress it or split it into smaller files, then send again. 

3/ Isolate blockers (add-ins/security scan) and rebuild the sending path 

• Start Outlook in Safe Mode: press Windows + R, type outlook.exe /safe, then press Enter. 
• Try sending the email again from Safe Mode; if it sends successfully, disable add-ins in normal mode: File > Options > Add-ins > COM Add-ins > Go > uncheck non-Microsoft add-ins, then restart Outlook. 
• If the message still sticks, create a fresh Outlook profile: open Control Panel > Mail > Show Profiles > Add, sign in to the account, set the new profile as default, then open Outlook and send again. 

4/ Contact IT administrator:    

Since your account is managed by your organization, please contact your IT administrator to review your permissions and policies. If the issue persists after these checks, ask your IT administrator to submit a support request directly to Microsoft Support team.         

They can raise a support ticket by visiting: Get support - Microsoft 365 admin | Microsoft Learn    

As community moderators, we appreciate your understanding that our access to internal development details is limited. Our primary role is to guide users toward the appropriate resources and support channels. While we may not have visibility into deeper backend analysis, we’ll continue doing our best to support you within the scope of our responsibilities.        

I hope this information is helpful. Please follow these steps and let me know if it works for you. If you have any updates regarding the issue, please feel free to share them with me.          

Thank you for your patience and your understanding. I look forward to continuing the conversation.   

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Use the following checks and fixes in Outlook Classic on Windows when messages with attachments stay in the Outbox:

1. Remove or reduce large attachments
   1. In Outlook, select Send/Receive > Work Offline to stop Outlook from trying to send.
   2. In the Navigation Pane, select the Outbox.
   3. For each stuck message:
      • Either delete it (select it and press Delete), or
      • Drag it to Drafts, open it, and delete or replace the large attachment.
   4. Go back online by selecting Send/Receive > Work Offline again.
   5. Resend the message with a smaller attachment or a link to the file.
   Some providers block messages above certain sizes (for example, >20 MB). If the attachment is large, remove it or follow the guidance in Reduce attachment size to send large files with Outlook.
2. Make sure Outlook is online
   1. In Outlook, select Send/Receive.
   2. Check the Work Offline button:
      • If it is highlighted (blue), Outlook is offline. Select it to go online.
   3. Select Send/Receive All Folders or Send All to push the Outbox messages.
3. Enable automatic sending when connected If messages only send when manually triggering Send/Receive (for example, pressing F9):
   1. Go to File > Options.
   2. Select Advanced.
   3. In Send and receive, enable Send immediately when connected.
   4. Select OK and test sending again.
4. If Outlook says it is transmitting and won’t let the message be edited
   1. Select Send/Receive > Work Offline.
   2. Close Outlook and wait a few moments.
   3. If Outlook does not close, press Ctrl+Alt+Delete, open Task Manager, go to the Processes tab, select outlook.exe, and choose End Process.
   4. Reopen Outlook, go to Outbox, and delete or edit the stuck message as in step 1.
   5. Turn off Work Offline and send again.
5. If the issue is specific to Cached Exchange Mode (advanced/admin scenario) When using an Exchange account in Cached Exchange Mode and messages stay in Outbox but the issue disappears in Outlook Safe Mode, a registry value can be the cause. The documented resolution is:
   1. Open Registry Editor.
   2. Navigate to: HKEY_CURRENT_USER\Software\Microsoft\Office\<x.0>\Outlook\Preferences (where x.0 is the Outlook version, for example 15.0, 14.0, 12.0).
   3. Delete the LoadTransportProviders DWORD value.
   4. Close Registry Editor and restart Outlook.
   Editing the registry is risky; it should be done only by an administrator or experienced user, and only after backing up the registry.

If, after these steps, messages without attachments send correctly but any message with an attachment still remains stuck, verify attachment size and provider limits first, then test with a very small file (for example, a small text file) to confirm whether the problem is purely size-related.

References:

• Outlook email stuck
• I can't send or receive messages in Outlook
• Outlook for Mac Help