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.

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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