Thunderbird Sending of the Message Failed

Summary: Thunderbird is widely used to manage emails from different accounts in one place. However, sometimes users may face the “Sending of the message failed” error while trying to send an email. This can happen because of incorrect SMTP settings, authentication problems, antivirus or firewall interference, a damaged profile, or issues with the local Thunderbird mailbox data. In today’s post, we will discuss the common reasons behind this error and different methods to troubleshoot it.

Also Read: Thunderbird ImportExportTools Add-on

Why Does Thunderbird Say “Sending of the Message Failed”?

There can be different reasons why Thunderbird fails to send an email. Let’s look at some of the common causes below.

• Incorrect SMTP server or port settings can prevent Thunderbird from connecting to the outgoing mail server.
• The selected authentication method may not match the requirements of your email provider.
• Incorrect or expired account credentials can cause authentication failures.
• Antivirus software or a firewall may block Thunderbird's connection to the mail server.
• A problem with the Thunderbird profile or local mailbox data can sometimes affect email operations.
• The outgoing mail server may be temporarily unavailable.
• A large attachment or message can also fail if it exceeds the email provider's size limit.
• Network connectivity problems may interrupt the connection while Thunderbird is sending the message.

How to Fix Thunderbird Sending of the Message Failed? Manual Methods

There are several methods you can try to resolve the Thunderbird sending of the message failed error. Follow the methods carefully and test Thunderbird after each one.

#1. Check SMTP Server Settings

The first thing to check is the outgoing SMTP configuration of your email account.

• Open Thunderbird.
• Click the Menu button and select Account Settings.
• Scroll down and select Outgoing Server (SMTP).
• Select the SMTP server associated with your email account.
• Click Edit.
• Verify the Server Name, Port, Connection Security, and Authentication Method.
• Make sure these settings match the requirements of your email provider.
• Save the changes and try sending the message again.

Note: Do not randomly change SMTP values. Use the settings provided by your email service provider.

Step 2. Check Your Account Password

Sometimes Thunderbird cannot authenticate with the outgoing mail server because the stored password is incorrect or outdated.

• Open Thunderbird's Account Settings.
• Check the account and SMTP configuration.
• If Thunderbird asks for your password while sending, enter the correct credentials.
• If you recently changed your email password, update the saved credentials in Thunderbird.
• Try sending a small test email.

If the problem was caused by incorrect authentication details, the email should now be sent successfully.

Step 3. Temporarily Check Antivirus or Firewall Interference

Security applications can sometimes interfere with Thunderbird's connection to an SMTP server.

• Check whether your antivirus or firewall is blocking Thunderbird.
• Make sure Thunderbird is allowed to access the internet.
• If your security software has email scanning enabled, check its configuration.
• Temporarily disable the relevant email-scanning feature only for testing, if appropriate.
• Try sending the email again.

Important: Do not leave your security software disabled unnecessarily. If Thunderbird works after changing the security configuration, add Thunderbird as an allowed application instead.

Step 4. Try Sending an Email Without an Attachment

A large or problematic attachment can also cause Thunderbird to fail while sending.

• Create a new email.
• Do not attach any file.
• Send a short test message to yourself.
• If the message is sent successfully, try sending the original email again with a smaller attachment.

This can help determine whether the problem is related to the message or attachment rather than Thunderbird's SMTP configuration.

Step 5. Check Thunderbird in Troubleshoot Mode

If extensions or customized settings are causing the problem, Thunderbird's Troubleshoot Mode can help identify the issue.

• Open Thunderbird.
• Click the Menu button.
• Select Help.
• Choose Troubleshoot Mode.
• Restart Thunderbird when prompted.
• Try sending an email again.

If sending works in Troubleshoot Mode, an extension, theme, or customized setting may be contributing to the problem.

What If Thunderbird Still Cannot Send Emails?

If the above methods do not resolve the problem, the issue may be related to the Thunderbird profile or locally stored mailbox data. This can become more difficult when the profile contains a large amount of email data or when you are already experiencing problems with the Thunderbird application.

In such situations, first create a backup of your Thunderbird mailbox data before making major changes to the profile.

Expert Way to Manage Thunderbird Mailbox Data

If the sending problem is accompanied by profile-related issues, corrupted local data, migration requirements, or difficulty accessing mailbox files through Thunderbird, SysTools Thunderbird Import Wizard can be considered as a professional way to manage and import Thunderbird-compatible mailbox data.

It can import MBOX to Thunderbird without requiring users to manually perform the complete import process through Thunderbird.

Key Features:

• Allows users to import MBOX files into Thunderbird profiles.
• Supports importing mailbox data without depending on the regular Thunderbird import process.
• Maintains the existing folder hierarchy during the import.
• Supports attachments and other email data.
• Provides options to select specific mailbox files or folders.
• Supports bulk importing of multiple MBOX files.
• Can be useful when users are facing difficulties with the Thunderbird application while managing local mailbox data.

This approach does not directly repair an SMTP or email-provider issue. Instead, it provides an alternative way to manage and import local mailbox data when the Thunderbird profile or application is creating difficulties.

Important Tips to Follow

• Verify the SMTP server, port, authentication, and connection security settings before changing your Thunderbird profile.
• Make sure your internet connection is stable.
• Check whether your email provider has any temporary service issues.
• Keep attachments within your provider's allowed size limit.
• Create a backup of your Thunderbird profile before making major changes.
• Do not delete the existing Thunderbird profile until you have confirmed that your mailbox data is safely accessible.
• If the issue continues after SMTP troubleshooting, consider testing the account in another email client to determine whether the problem is specific to Thunderbird.
• If you need to move or re-import local mailbox data, use a dedicated import solution rather than repeatedly modifying the original profile.

Conclusion

The “Sending of the message failed” error in Thunderbird can occur because of incorrect SMTP settings, authentication problems, firewall or antivirus interference, attachment issues, or problems with the local Thunderbird profile. Start with the basic SMTP and account checks before making changes to your profile.

If the problem is connected to managing or importing local mailbox data, provides a professional way to import MBOX files into Thunderbird profiles without relying entirely on the application's manual import process. This can be particularly useful when dealing with profile migration or local mailbox management.