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Timely sending and receiving emails is the backbone of any email client. But if that gets hampered, the entire communication cycle comes to a major halt which can turn into a loss-making incident for many companies. Nobody wants to be part of such a situation.

When you use Microsoft 365 account, it is managed in the Outlook application for the transfer of emails. But sometimes during a problem in the email server, the sent emails get stuck in the Outbox folder and an error message is displayed- “Office 365 messages stuck in Outbox”. This issue can be tolerated if the emails remain in Outbox folder for a few minutes, but if it is taking more time, then it can turn into a nightmare.

The error is a common one and can occur due to numerous reasons. To prevent this situation, you must read along to understand its causes and methods to fix it quickly.

What is the Outbox folder?

Some of you must have just started using Outlook and not aware about all the folders which are present in this application. Outbox is often referred as a ‘holding folder’ since it holds an email until the time (span of a few microseconds) it gets automatically sent. Many a times, emails get stuck in this folder until the user manually clicks on Send or Receive to transfer the message. Outbox is listed on the left side panel of the Outlook application.

Causes of “Office 365 messages stuck in Outbox”

There are several reasons which are responsible behind all the trapped emails in Outbox. A few common ones have been listed below-

  • Connection issues-
    The prime reason for most of the errors is a poor connection whether it is with the router, service provider, email server or settings. Due to a limited connection, emails are not being sent and continue to stay in the Outbox.
  • Heavy attachment emails-
    Sending photos, videos and other documents through emails is a frequent practice but Outlook cannot handle if you try to send a large sized attachment. The maximum limit for any email attachment is 20MB.
  • Incorrect configuration-
    These errors also occur when the authentication or security settings have been incorrectly configured in Office 365 and Outlook.
  • Interference of other software-
    Often some other software like anti-virus program begin to interfere with the currently running platforms. They are scanning and blocking some important ports and emails just by considering them as a kind of threat.
  • Opening a stuck email-
    In case you open the email while it was stuck in the process of sending, then the default setting of Outlook will immediately stop it.
  • Other reasons-
    Some other minor causes include corruption in files, incorrect date and time settings, restrain due to add-ins, no default email account and Outlook is being used with some another program.

We have some quick fixes which will help you deal with this condition where “Office 365 messages are stuck in Outbox.”

Fixes for “Office 365 messages stuck in Outbox” state
  1. Delete/Send the email stuck in Outbox if it opens without error
  2. Send the emails stuck in Outbox if it does not open and shows error
Case I – Emails Stuck In Outbox And Open Without Error
  1. Delete: First of all, open the email client application for Office 365 and go to the Outbox folder. Click on it and select the displayed emails, right-click on it, and select the Delete option. The stuck emails will get deleted and vanish from the Outbox folder.
  2. Send: Go to the Outbox folder. Now try to open the emails one by one by double-clicking them and then send them using Send option at the top-left side of the interface.
Case II- Emails Stuck In Outbox And Fail To Open

Sometimes the email does not open, but shows errors like “Sorry, we have trouble opening this email item….”. This can happen if Outlook is connected to the server, and the online server keeps trying to send the large-sized emails.

To disconnect email client from the configured email server, just click on the Send/Receive tab at the top of the menu bar and then click Work Offline option.

On the status bar, you can see the status is changed from Connected to Working Offline.

Now, try to open the emails in the Outbox folder again, if it gets opened, send or delete the email as per your requirement.

And, if it still shows the error and fails to open, close the Outlook application. Sign out from the Windows, then sign in and restart the Outlook application.

Now try dragging the emails from the Outbox folder to the drafts folder. Now again go to Send/Receive tab on Outlook and click Work Offline. Then, in the drafts folder, you can access or open the emails; click the Send option to send it directly to the recipients.

Note: If the emails contain large attachments, then use Save All option to save them to a network or shared location. Then copy the link of the folder path (of the shared network where the attachments are stored). Paste this link to the email content and remove the attachment from the email. Then, send this email to the recipient avoiding any further issue.

Quick solutions for emails getting stuck in Outbox-

If the above methods have not worked well for you, then other minor causes can be behind this issue. You can solve it by giving a try to these quick fixes:

  • Check if you have exceeded the per day email sending limit.
  • Run a thorough scan on the speed and bandwidth of your Wi-Fi and router connection.
  • No rule related to delay in sending should be applied on the email account.
  • Resolve any issue with the Office 365 and Outlook servers.
  • Check if the service provider is blocking any outgoing port.
  • Reset the system’s time and date to the correct one.
  • Keep all the platforms updated with their latest versions.
  • Only sent healthy files as attachments.
  • Ensure that MS Outlook is working in the Online mode.
  • The port number is not blocked and working well.
  • Resend email with small sized or no attachment.
  • Run Outlook in the Safe Mode.


The error “Office 365 messages stuck in Outbox” has become a common one now. This can be caused due to several reasons but needs to be resolved only with the right approach. If the problem remains in the system, you should at least take backup of all your Office 365 data by using the Kernel Office 365 Backup & Restore software. It will save the mailbox data in a PST file, and when your account shows any error and you require to remove the account, you can use the PST file to restore Office 365 mailbox items.