Outlook for Mac Email Stuck in Outbox? Here’s How to Fix It

Are your emails stuck in the Outbox? If yes, you are not alone. It is one of the most frustrating but common issues. It is one of the most reported issues among Mac users while running MS Outlook. What the query – Outlook for Mac Email Stuck in Outbox indicates is that Outlook is unable to send the messages to the mail server due to some connectivity or other software-related issues. We are listing out all the causes that lead to this issue and how we can overcome them without losing any data.

In the guide, you will get the causes and the respective working fixes from quick to advanced solutions. Go through each of the methods one by one, get emails out of the Outbox and complete the send process.

What is the Use of the Outbox in Outlook?

Outbox in Outlook is used to handle the message sending process. It gives Outlook a place for the emails to queue before they are delivered. It works when you are offline; that is, emails stay in the Outbox and are sent automatically once you are back online. We can edit or delete it before sending it from the Outbox folder. If you want to send multiple emails, they will be queued in the Outbox and sent one by one.

Why is Your Outlook for Mac Email Stuck in Outbox?

Before we go to the fixes, understand what is causing the issues. Outlook for Mac queues the emails in the Outbox while the email account establishes a server connection and then sends the messages.

When the messages get stuck there, that means something has intercepted the transmission and blocked the process. Here are some common causes: Outlook Mac emails stay in the Outbox.

• The server has an attachment size limit; if the files are oversized, then the message will not pass through.
• If the message is corrupted, Outlook cannot process it properly.
• Unstable internet connection during the attempt to transfer the emails.
• Authentication failures, i.e., wrong password or expired OAuth token.
• Incorrect or expired outgoing mail server settings (SMTP).
• Offline mode is enabled accidentally and not going back to online – check the article: Outlook Stuck in Offline Mode
• Outdated Outlook might have some bugs.
• Antivirus or firewall software is blocking Outlook’s outbound connections.

How to Fix the “Outlook Mac Emails Stuck in Outbox” – Quick Checks First

First, we will go through some quick solutions before we move on to advanced fixes. Many stuck emails and Outlook issues are resolved mostly with these steps:

Check Internet Connection

Open Safari or Chrome and visit any webpage. The internet is not the issue. If not, troubleshoot the network; Outlook cannot proceed with sending the emails from Outlook without an internet connection.

Check whether Outlook is in Offline Mode

Mac Outlook can sometimes be in offline mode due to various reasons.

1. Open Outlook for Mac.
2. Look at the menu bar and click on Outlook.
3. Check for Work Offline in the dropdown menu.
4. Click on Work Offline to remove it.
5. Confirm Outlook is back online.

Fix 1: Delete and Resent the Email Stuck in the Outbox

Start with the simple fix by deleting the stuck message and composing a fresh one:

1. Open Outlook for Mac, click on “Outbox” in the left panel.
2. Right-click the message and select the Delete option from the menu.
3. If the message is not deleted, try switching to offline first and deleting it. Then go back online.
4. Compose a new email and attempt to send it.

If the new message is sent successfully, the original message was corrupted. If the message is stuck again in the Outbox, then the issue is systemic and requires more technical fixes.

Fix 2: Reduce the Email Attachment Size

The common reason why emails get stuck in the Outbox is due to the attachment size. If the attachments exceed the maximum allowed size by the mail server or Microsoft 365 policy.

• Microsoft 365 has a default maximum size of 25 MB.
• An on-premises Exchange server has a limit by organisation configuration – 10-35 MB.
• A Gmail account configured in Outlook imposes a 25 MB limit.

How to resolve “Outlook for Mac Email Stuck in Outbox” by compressing attachments

1. Delete the stuck message from the Outbox.
2. Complete attachment – right click > compress on Mac.
3. If the files are still large, upload them to the OneDrive, Google Drive, SharePoint, or Dropbox.
4. Share the file as a link in the email body instead of a direct attachment.
5. Resend the email.

Fix 3: Force Outlook to Send via Offline Mode

This method is to re-attempt sending a queued message by toggling the offline state:

• Go to Outlook Menu > Work Offline.
• Wait a few seconds.
• Go to the Outlook menu > Work Offline again.
• Outlook will immediately attempt to send the queued Outbox message.

It usually works because it resets Outlook’s connection to the mail server, clearing any temporary connection hang that prevents the send.

Fix 4: Update the Mac Outlook Application to Fix “Outlook for Mac Email Stuck in Outbox”

The Outbox issue is caused by bugs in older versions of Outlook that Microsoft has since patched. Keep Outlook updated to fix and prevent any issues in the future.

• Open the MS Office application.
• Go to the Help menu at the top.
• Click “Check for Updates”
• The Microsoft AutoUpdate tool will open and scan for any updates.
• Click “Update All” and allow the installation to complete.
• Relaunch Outlook after the update and check whether the Outbox issue is resolved.

If there is no “Check for Updates” in the Help menu, you may have installed Outlook from the Mac App Store.

Fix 5: Rebuild Outlook Profile

A corrupt Outlook profile is a common and often overlooked cause of persistent Outbox problems. Rebuilding the profile forces Outlook to re-establish the account connections from scratch.

• Quit Outlook entirely.
• Open the Finder and navigate to: ~/Library/Group Containers/UBF8T346G9.Office/Outlook/Outlook 15 Profiles
• Right-click the current profile folder and rename it.
• Relaunch Outlook – it will prompt you to set a new profile.
• Enter the account credentials and allow Outlook to sync.

Rebuilding the profile does not delete the emails if you use Exchange, Microsoft 365, IMAP, or Gmail – they will resync from the server.

Tip: Locally stored items in the On My Mac folder will not be in the new profile. So make sure to back it up first. You can export your data using Outlook’s built-in export feature or use the Email Backup Tool to save all the important emails before rebuilding the Outlook profile.

Fix 6: Verify and Correct SMTP Outgoing Mail Server Settings

If the email account’s SMTP settings are wrong, Outlook cannot send messages, and the email might stay in the Outbox. It is especially common after password changes, organisational IT policy updates or when setting up a new account.

1. In Outlook, go to the Outlook menu > Preferences > Accounts.
2. Select the email account that has a stuck message in the Outbox.
3. Click “Advanced” or the settings icon.
4. Verify the following Outgoing Mail Server (SMTP) settings are correct:
   • Server address: provided by email host.
   • Port: usually 587 (TLS) or 465 (SSL) -avoid port 25, which is often blocked by ISPs.
   • Authentication: should match the account type.
   • SSL/TLS: should match the server requirement
5. If you changed the email password recently, update it as well.
6. Click Ok and attempt to send a test email.

Fix 7: Sign Out and Sign in to the Account

Microsoft 365 and Exchange account, the authentication token can expire, causing issues, including email send failures that appear in the Outbox. Sign out and sign back in, as it refreshes the token.

• In Outlook, go to the Outlook menu > Preferences > Accounts.
• Select Microsoft 365 or Exchange account
• Click on the minus (-) button to remove or sign out.
• Click the remove.
• Click the minus (+) button to add the account back.
• Enter the email address and follow the authentication instructions.
• Allow Outlook to complete the sync and test sending again.

Fix 8: Check Antivirus and Firewall Settings

Security software can intercept and block Outlook’s outbound connections on port 587 or 465, causing messages to queue in the Outbox.

• Temporarily disable the antivirus or firewall software.
• Attempt to send a test email in Outlook.
• If the emails are sent successfully, the security software is the issue.
• Now, re-enable the security software and add Outlook as a trusted application.
• Or create an exception for port 587 or 465.

Fix 9: Clear Outlook Cache to Fix “Outlook for Mac Emails Stuck at Outbox”

Outlook maintains a local cache of the account data, messages, and calendar items. When the cache becomes corrupted, it can interfere and cause the messages to get stuck in the Outbox. Clear the Cache as a force sync to fresh.

• Quit Outlook completely.
• Open Finder, click Go in the menu, hold the Option key and click Library.
• Navigate to: ~/Library/Caches/com.microsoft.Outlook.
• Select the files in the folder and move them to the trash.
• Go to: ~/Library/Containers/com.microsoft.Outlook/Data/Library/Caches
• Delete the files.
• Relaunch Outlook and now try sending emails.

Fix 10: Finally, Remove and Reinstall Outlook for Mac

If all the other fixes failed, start fresh by doing a clean reinstallation of Outlook. It resolves any deep application-level issues, including corrupt installation files and persistent bugs.

1. Quit the Outlook application.
2. Open Finder > Applications.
3. Drag Microsoft Outlook to the Trash and empty the Trash.
4. Restart the Mac to clear the Temp files.
5. Download the latest version of Outlook from the official Microsoft website and install it via the Mac App Store.
6. Open Outlook and sign in to the account.
7. Allow Outlook to sync fully, then try sending the emails again.

Ensure a complete reset of Outlook, which eliminates any issues causing emails to remain stuck in the Outbox.

FAQs

Q) Why are the emails in the Outbox but not in the Sent folder?

A) This means the Outlook attempted to send the message but did not receive the delivery confirmation from the server. The message in the Outbox as Outlook continues retrying.

Q) Can I open and edit the stuck message in the Outbox?

A) Yes. Double-click the stuck messages in the Outbox to open them. You can edit the content, remove attachments, or change recipients. After editing, click Send Again. Some versions of Outlook do not allow it, so you need to keep Outlook offline.

Q) Is there a way to force send all stuck Outbox messages at once?

A) Yes. Go to Outlook menu > Work Offline to enable offline mode, wait a few seconds, then turn off offline mode. This forces Outlook to flush the Outbox and retry the pending sends simultaneously. Press Command + K on Mac as a keyboard shortcut for Send and Receive All.