Thunderbird Sending of the Message Failed

Sometimes Thunderbird cannot authenticate with the outgoing mail server because the stored password is incorrect or outdated.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