Outlook: The Message Could Not Be Sent - An Error Has Occurred

Knowledgebase

Outlook: "The Message Could Not Be Sent. An Error Has Occurred."

This error appears in Microsoft Outlook when the application is unable to communicate with your outgoing (SMTP) mail server. There are several common causes and fixes.

Check Your Outgoing Server Settings

The most common cause is incorrect SMTP settings. Verify the following in your Outlook account configuration:

Outgoing mail server (SMTP): mail.yourdomain.com
Port: 465 (SSL) or 587 (TLS) or 26 (alternate, useful if your ISP blocks port 25)
Encryption: SSL/TLS
Authentication: Must be enabled. Go to More Settings > Outgoing Server tab and check "My outgoing server requires authentication."

ISP Blocking Port 25

Many internet service providers block port 25 to prevent spam. If your outgoing mail is not working, try switching your SMTP port to 587 or 26. This resolves the issue in most cases.

Antivirus or Firewall Interference

Some antivirus programs and firewalls scan outgoing email traffic and can interfere with Outlook. Try temporarily disabling your antivirus email scanning feature to see if the error goes away. If it does, add an exception for Outlook in your security software.

Corrupt Outlook Profile

If your settings are correct but the error persists, your Outlook profile may be damaged. Try creating a new mail profile through Control Panel > Mail > Show Profiles > Add. Set up your email account again in the new profile and test sending.

Large Attachments

If the error only occurs when sending messages with attachments, the file may exceed the server attachment size limit. Try sending without the attachment or compressing the file first. The default maximum attachment size is typically 50 MB.

If none of the above resolves the issue, please open a support ticket with the exact error message and your email settings, and we will help troubleshoot further.