The ‘Outlook couldn’t send this message’ error is not tied to a single cause. Outlook relies on several components working together correctly. Your internet connection must be stable, your email account settings must match your provider’s requirements, and Outlook must be able to communicate with outgoing mail servers.
When one of these elements stops functioning properly, Outlook may prevent emails from being sent. Sometimes the issue affects only one message, while in other situations every outgoing email remains stuck in the Outbox folder.
The exact reason can vary depending on whether you use a personal account, such as Outlook.com, Gmail, Yahoo Mail, or a business account managed through Microsoft Exchange or Microsoft 365. That is why it is important to work through the troubleshooting process step by step instead of guessing the cause.
In this guide, I will explain the entire process step by step so you can resolve this issue and send emails without interruption.
Fix ‘Outlook Couldn’t Send This Message’ Error
If Outlook displays the ‘Outlook couldn’t send this message’ error, the problem is usually caused by an unstable internet connection, incorrect email account settings, oversized attachments, corrupted Outlook files, or temporary issues with the mail server. Verifying your connection, checking account settings, repairing Outlook data files, and updating the application can usually resolve the issue and restore normal email sending functionality.
Let’s explore the process in detail!
Step 1: Verify Your Internet Connection
The first thing you should check is your internet connection. Outlook requires a stable connection to communicate with mail servers. If your connection is weak or interrupted, Outlook may fail to send messages and display an error.
Open your web browser and visit a few websites. If pages load slowly or fail to open, your internet connection may be the source of the problem.
If you are using WiFi, try disconnecting and reconnecting to your network. You can also restart your router and modem. If possible, connect your computer using an Ethernet cable to see if the issue disappears.
After confirming that your internet connection is working properly, return to Outlook and attempt to send the message again. Many users discover that the problem resolves immediately after restoring network connectivity.
Step 2: Check Whether Outlook Is Working Offline
Outlook includes a feature called Work Offline. When enabled, Outlook stops communicating with mail servers, preventing messages from being sent or received.
Open Outlook and select the Send/Receive tab. Look for the Work Offline button. If the option appears highlighted, Outlook is currently disconnected from the server.
Click the button once to disable offline mode. Wait a few moments for Outlook to reconnect to the mail server.
Once the status changes back to online mode, try sending your email again. This simple adjustment is often overlooked and can instantly solve the problem.
Step 3: Remove Large Attachments
Large attachments are a common reason for email delivery failures. Most email providers place limits on the size of outgoing messages.
Open the email that failed to send and examine any attached files. Large videos, presentations, ZIP archives, and high-resolution images can exceed sending limits.
Try removing the attachment and sending the message again. If the email sends successfully, the attachment size was likely the issue.
Instead of attaching large files directly, consider uploading them to a cloud storage service and sharing a download link. This approach helps avoid size restrictions while making file sharing easier.
Step 4: Review Your Email Account Settings
Incorrect account settings can prevent Outlook from communicating with outgoing mail servers.
Open Outlook and go to File. Select Account Settings, then choose Account Settings again. Highlight your email account and select Repair or Change depending on your Outlook version.
Verify that the incoming and outgoing server information matches the settings provided by your email provider. Pay special attention to the SMTP server, port numbers, and encryption settings.
Even a small typo in the server address or authentication settings can trigger the ‘Outlook couldn’t send this message’ error. Correct any discrepancies and save your changes before testing email delivery again.
Step 5: Empty the Outlook Outbox
A corrupted or stuck email in the Outbox folder can prevent other messages from being sent.
Open the Outbox folder and look for messages that remain unsent. If you find a message that has been stuck for an extended period, open it and save a copy if necessary.
Delete the problematic message and close Outlook. Reopen the application and try sending a new test email.
In many cases, removing a stuck message allows Outlook to resume normal sending operations.
Step 6: Repair Outlook Data Files
Outlook stores email information in data files such as PST and OST files. If these files become corrupted, sending and receiving issues can occur.
Microsoft includes a built-in repair utility called Inbox Repair Tool (SCANPST.EXE). Locate the tool on your computer and run it.
Browse to your Outlook data file and start the scanning process. The tool will identify and repair detected issues.
Once the repair is complete, restart Outlook and test email functionality again. Repairing damaged data files often resolves persistent Outlook errors.
Step 7: Disable Problematic Add-Ins
Third-party add-ins can interfere with Outlook’s normal operation. Some add-ins may block outgoing messages or create conflicts that trigger sending errors.
Open Outlook and select File, then Options, followed by Add-ins.
At the bottom of the window, choose COM Add-ins and select Go.
Temporarily disable all add-ins and restart Outlook. Attempt to send an email.
If the message sends successfully, one of the disabled add-ins is likely responsible. Re-enable add-ins individually until you identify the problematic one.
Step 8: Update Microsoft Outlook
Running an outdated version of Outlook can lead to compatibility issues and software bugs.
Open Outlook and select File. Navigate to Office Account and choose Update Options. Select Update Now.
Allow Microsoft Office to download and install available updates. These updates often contain bug fixes and performance improvements that address email sending problems.
After the update completes, restart your computer and test Outlook again.
Step 9: Create a New Outlook Profile
Sometimes an Outlook profile becomes damaged, causing repeated email issues.
Open the Control Panel and select Mail. Choose Show Profiles and select Add to create a new profile.
Follow the setup wizard to add your email account. Once the new profile is created, configure Outlook to use it as the default profile.
Launch Outlook using the newly created profile and test email sending functionality.
A fresh profile can eliminate hidden configuration problems that are difficult to diagnose through standard troubleshooting.
Step 10: Check for Mail Server Issues
Sometimes the problem is not on your computer at all. The issue may originate from your email provider’s servers.
If you use Outlook.com, Microsoft 365, Gmail, Yahoo Mail, or another hosted email service, visit the provider’s status page and check for service disruptions.
Temporary outages can affect outgoing mail delivery. In these situations, the best solution is simply waiting until the provider restores normal service.
You can also attempt to send an email from your provider’s webmail interface. If webmail cannot send messages either, the issue is likely server-related rather than Outlook-related.
Step 11: Repair Microsoft Office
If Outlook continues displaying the error, repairing the Office installation may help.
Open Settings and navigate to Apps. Locate Microsoft Office or Microsoft 365 in the application list.
Select Modify and choose Quick Repair. If the issue remains, perform an Online Repair.
The repair process replaces damaged program files and restores Outlook components to a healthy state.
After the repair finishes, restart your computer and test Outlook once more.
FAQs
Why does Outlook say it couldn’t send my message?
This message usually appears when Outlook cannot connect to the outgoing mail server, encounters incorrect account settings, detects oversized attachments, or experiences issues with Outlook data files.
Can a large attachment cause Outlook to send errors?
Yes. Most email providers enforce attachment size limits. If your attachment exceeds the allowed size, Outlook may fail to send the message and display an error.
How do I know if my Outlook profile is corrupted?
Signs of profile corruption include repeated sending failures, synchronization issues, missing folders, unexpected crashes, and persistent account errors. Creating a new profile is often the fastest way to test for this problem.
Will repairing Outlook delete my emails?
No. Standard repair procedures, including Office Repair and the Inbox Repair Tool, are designed to preserve your email data while fixing application issues.
Should I remove and re-add my email account?
If basic troubleshooting does not work, removing and re-adding the account can help resolve configuration issues. However, creating a new Outlook profile is often the more effective long-term solution.