Fix Undeliverable Emails in Outlook [Tested Methods 2024]

Written By Steven Arends

After spending so much time and effort composing an email, you finally click Send. But, instead of the message going through, it comes back to you like a boomerang saying it’s Undeliverable can be frustrating.

It is a common issue in Outlook and can occur for several reasons.fix-undeliverable-emails-in-outlook-b

But whatever the cause of the problem is, this article covers all the steps you need to perform and all the settings you need to check to solve undeliverable emails in Outlook.

Let’s begin!

Why are Your Emails Coming Back as Undeliverable in Outlook?

Your emails are returning as undeliverable in Outlook mainly because they conflict with your account settings. Disabling scheduled send/receive, using a rule that stops you from sending messages or a corrupted profile, can label your emails as undeliverable.

Below I’ve listed all the reasons why your emails are not going through, so you may know what to do to solve this issue.

Here’s why your emails are coming back as undeliverable in Outlook:

  • Corrupted email profiles.
  • Connecting too many profiles to your Outlook account.
  • Confliction with Firewall settings.
  • Setting bad email rules.
  • Outlook is set to work offline.
  • No internet connection or unstable internet.
  • Using the wrong username and password.
  • Problems with junk email settings.
  • Your email address has a low reputation score.
  • Recipient’s mailbox is full.
  • The message is too big.
  • Incorrect domain of the recipient’s email address.
  • Recipient server error.
  • The recipient can only receive emails from specific addresses.

Now that you know why you cannot send messages in Outlook, let’s troubleshoot the problem.

Follow our guide to fix Outlook rules not running when closed.

How to Solve Undeliverable Emails in Outlook

To stop undeliverable emails in Outlook, check your account settings and incoming & outgoing server ports and make sure they are correct. Also, remove unnecessary profiles from Outlook and delete the cache, as bad files can cause this issue.

Follow the instructions below to troubleshoot undeliverable emails in Outlook.

Here are the steps to solve undeliverable emails in Outlook:

1. Check Your Account Credentials

Using the incorrect account credentials won’t let you send messages in Outlook. Check and make sure there are no typos in your account information.

Here’s the process to check your account settings:

  • Open Outlook on your computer.
  • Select File from the upper left corner.outlook-file
  • Choose Account Settings > Account Settings. outlook-account-settings
  • Double-click on your account.outlook-email-account
  • Check all your account credentials and make sure they are correct.outlook-email-account-credentials

If your account information is incorrect, go to the following section, where I’ve explained how to change your account credentials.

Also read how to automatically forward emails in Outlook?

2. Modify Your Account Information

Change and modify your account information from Server Settings in Outlook.

Here’s how to modify your account information:

  • Launch Outlook.
  • Select File at the top left.outlook-file
  • Choose Account Settings > Server Settings. outlook-server-settings
  • Update the Incoming mail & Outgoing mail information.outlook-incoming-outgoing

3. Check the Junk Mail Settings

If your Outlook Junk settings are set to a restrictive option, it won’t allow you to receive & send certain emails. It can also put your emails in different folders. So, choose a less aggressive junk filtering option.

Here are the steps to check the junk mail settings:

  • Open Outlook.
  • Expand Junk and click on Junk E-mail Options.outlook-junk-options
  • Set either the No Automatic Filtering or Low filtering option.outlook-junk-no-filter
  • Go to the Blocked Senders tab and make sure no user is blocked in there that you are trying to send emails to. outlook-remove-block

Check out our separate post about to fix Outlook rules not working on phone.

4. Test Your Account Settings

Windows has a dedicated program that runs a test on your email account and checks for errors. Perform the test and see the result.

Here’s how to test your account settings:

  • Search for the Control Panel and open it. control-panel-open
  • Change View by to Large icons and select Mail (Microsoft Outlook). control-panel-mail
  • Choose Email Accounts.mail-setup-accounts
  • Select your email address or username and click on Change. mail-account-change
  • Select Test Account Settings and wait for the test to finish. mail-test-account

If the test runs successfully, you don’t need to change anything in your account. However, in case of any errors, you need to modify some settings.

Related content you should read about how to change client-only rule to server in Outlook.

5. Change Incoming & Outgoing Server Ports

Open your email account information from the Control Panel and make sure the Incoming & Outgoing server ports are correct.

Here’s the process to change your account settings:

  • Open the Control Panel and choose Mail. control-panel-mail
  • Click on Email Accounts. mail-setup-accounts
  • Choose your account and click on the Change button.mail-account-change
  • Check and modify the User Information, Server Information and Logon Information.
  • Select More Settings. mail-account-settings
  • Go to the Advanced tab and set the Incoming server port to 993 and the Outgoing server port to 465. outlook-incoming-outgoing-port
  • Click OK.

6. Check Your Outlook Rules

Sometimes, you can have complex rules set up that can restrict email addresses that you are trying to receive messages from or send emails to. So review and remove the rules that are blocking you.

Here are the steps to check your Outlook rules:

  • Open the Outlook app on your device.
  • Go to File from the top-left corner.outlook-file
  • Select Manage Rules & Alerts. outlook-rules-alerts
  • Choose the rule that’s blocking you and click on Delete. outlook-rules-delete
  • Select Yes to confirm your decision. outlook-rules-delete-yes
  • Click the Apply button, then OK. outlook-rules-delete-apply

7. Remove Unused Email Accounts & Profiles

Adding too many email accounts and profiles on your Outlook can conflict and cause problems. Remove the accounts you don’t need.

Here’s the process to remove unused email accounts & profiles from Outlook:

  • Search for the Control Panel and open it. control-panel-open
  • Choose View by as Large icons and select Mail (Microsoft Outlook).control-panel-mail
  • Click on Email Accounts. mail-setup-accounts
  • Pick the accounts you don’t use and click on Remove. mail-account-remove
  • Select Yes to confirm the removal process.mail-account-remove-yes
  • Close the Account Settings window. mail-account-clos
  • Choose Show Profiles on the Mail Setup dialog box. mail-show-profiles
  • Select the profiles you don’t need and click the Remove button.mail-profile-remove
  • Click on Yes to confirm your decision. mail-profile-remove-yes

8. Check Outlook Send/Receive Settings

If you’ve disabled the scheduled send/receive option in Outlook, it can stop you from sending messages. So, ensure it is turned on.

Here’s how to check Outlook send & receive settings:

  • Launch Outlook.
  • Proceed to the Send/Receive tab.
  • Expand Send/Receive Groups and ensure the Disable Scheduled Send/Receive option is unchecked. outlook-send-receive-scheduled
  • Select Define Send/Receive Groups. outlook-send-receive-define
  • Check the boxes for Include this group in send/receive and Schedule an automatic send/receive. outlook-send-receive-options
  • Close the Send/Receive Groups window.

9. Clear Outlook Cache

Corrupted cache files can cause email delivery issues in Outlook. Delete the cache and let the app create new files.

Here’s the method to clear Outlook cache files:

  • Close Outlook if it’s running.
  • Right-click on the Windows icon, choose Run or press the Win + R
  • Type %localappdata%\Microsoft\Outlook in the text field and press Enter. windows-run-outlook
  • Open the RoamCache folder.outlook-roamcache-folder
  • Select all the files and remove them.outlook-roamcache-file-delete
  • Open the Outlook application, and the files will be recreated automatically.

10. Create New Outlook Profile

If your Outlook profile gets corrupted due to malware or bugs, you’ll face problems such as undeliverable messages. In that case, you must make a new outlook profile.

Here’s the process to create a new Outlook profile:

  • Make sure Outlook is not running.
  • Open Control Panel and select Mail. control-panel-mail
  • Click on Show Profiles. mail-show-profiles
  • Select Add.mail-setup-profiles-add
  • Provide a profile name and click on the OK button. outlook-new-profile
  • Give your name, email address & password and click Next. outlook-new-profile-setup
  • Select Finish.
  • Open the Mail dialog box again.
  • Pick the newly created profile, choose the Always use this profile option and click OK. outlook-new-profile-run

Once you’ve set up your profile, you can back up and transfer all your emails there.


Why is Outlook saying my email is undeliverable?

Outlook says your email is undeliverable because you have disabled scheduled send/receive, using a rule that blocks messages, using a corrupted profile or using the wrong incoming & outgoing server ports.

Where do undeliverable emails go in Outlook?

Undeliverable emails go into the Sent folder even though the recipient doesn’t get the emails.

How do I stop Outlook from blocking emails?

Follow the steps below to stop Outlook from blocking emails:

  • Open Outlook.
  • Expand Junk and click on Junk E-mail Options.
  • Go to the Blocked Senders tab.
  • Make sure no user is blocked in there that you are trying to send emails to.

Final Thoughts

Undeliverable emails in Outlook can happen due to many different reasons regarding your and the recipient’s account settings.

But in this article, I’ve described all the correct settings you need to apply to fix this issue. Implement all the steps I’ve provided here, and you won’t see undeliverable error messages anymore.

Which process has resolved your issue? Let me know in the comments below.

About The Author
Steven Arends is a computer science graduate and tech enthusiast with over 10 years of experience in the field. He has a vast collection of computer hardware and loves exploring the latest advancements. As a contributing author to 10Scopes, Steven shares his expertise to make the world of technology more accessible and easier to understand for all readers.

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