How to Fix “Sending of the Message Failed” in Thunderbird?

Running into the “sending of the message failed thunderbird” error can be incredibly frustrating, especially when you need to send an important email urgently. This issue is common for Thunderbird users because the error can appear for many different reasons, including server misconfiguration, blocked ports, authentication problems or a weak internet connection. The good news is that this problem is fixable with a few careful adjustments, and you do not need technical expertise to solve it. This guide walks you through the most reliable and human-friendly ways to understand and fix the error quickly.

The first step in fixing this issue is identifying why Thunderbird is unable to send the message. The most common cause is an incorrect outgoing server setting. Your SMTP server details must match the requirements of your email provider. If the server address, port, encryption or authentication type is incorrect, Thunderbird rejects the message and displays the error. To fix this, open your Thunderbird account settings, find the outgoing server section and verify the SMTP server name, encryption type and authentication method. Most providers require TLS encryption and a specific port, so check those carefully. If even one element is wrong, the message will not send.

Another frequent reason for the “sending of the message failed thunderbird” message is a blocked port. Many antivirus programs and firewalls block email ports to prevent spam or harmful activity. If your firewall blocks your SMTP port, Thunderbird cannot reach the outgoing server. To solve this, temporarily disable the firewall or antivirus and try sending the email again. If the email goes through, re-enable your protection and add Thunderbird as an allowed or trusted application. This ensures that your system remains secure while still allowing Thunderbird to send messages normally.

Sometimes, the issue is caused by authentication errors. Thunderbird may not be passing the correct username or password to the mail server, especially if you recently changed your password or if your email provider requires OAuth login. To fix this, remove the saved password from Thunderbird’s password manager and re-enter your updated credentials. If your provider uses modern authentication, you may need to complete a browser-based login before Thunderbird allows message sending again.

Another factor behind the “sending of the message failed thunderbird” problem is an unstable or restricted internet connection. Many networks block outgoing email ports to avoid abuse, especially public WiFi hotspots. If you are connected to a network that restricts SMTP traffic, Thunderbird will fail to send your mail even if your settings are correct. Switching to another internet connection or using a mobile hotspot can help confirm if the issue is related to network restrictions. Once you confirm this, contact the network administrator or send messages only from networks that allow SMTP traffic.

Some users experience this error because their email provider limits the size of sent messages. When you attach large files, the server may reject the message without a clear explanation. Thunderbird then displays the “sending of the message failed thunderbird” alert. You can compress the attachments, upload them to a cloud storage service or reduce the file size to stay within your provider’s sending limits. This simple adjustment often solves the issue instantly.

Another overlooked cause is incorrect sender identity settings in Thunderbird. If the email address in your account identity does not match the address authorized by the outgoing server, the server will block the message. Verifying that the sender email, reply-to address and SMTP configuration are aligned helps avoid this mismatch. In some cases, users accidentally select the wrong outgoing server when managing multiple email accounts, which also leads to this error.

If none of these solutions work, the problem may be with the email provider itself. Servers sometimes experience outages or temporary disruptions. When the server is down, Thunderbird cannot connect, and the error appears even if your settings are correct. Checking your provider’s status page or waiting a little while often resolves the issue without further action. Trying again after the server stabilizes is a practical approach.

To prevent the “sending of the message failed thunderbird” error in the future, make sure your settings remain updated. If your provider changes recommended ports or encryption methods, update your Thunderbird configuration accordingly. Regularly checking your firewall permissions, keeping Thunderbird updated and avoiding oversized attachments also help maintain smooth email sending.

Below are some common questions users ask while dealing with this issue.

FAQ

Why does Thunderbird say “sending of the message failed”?
This happens when Thunderbird cannot connect to the outgoing server due to wrong settings, blocked ports, authentication issues or a network restriction.

How do I fix SMTP server errors in Thunderbird?
Verify your SMTP server name, port, encryption type and authentication settings. Make sure they match your email provider's requirements.

Can my antivirus cause this error in Thunderbird?
Yes, antivirus or firewall software may block SMTP ports. Adding Thunderbird as an allowed app usually solves the problem.

Why can I receive emails but not send them in Thunderbird?
Receiving uses IMAP or POP, while sending uses SMTP. If SMTP settings are incorrect or blocked, sending fails even if receiving works.

Does email size affect sending in Thunderbird?
Yes, if your attachments exceed your provider’s limits, the server can reject the message and trigger the error.

By understanding the underlying causes and applying these practical solutions, fixing the “sending of the message failed thunderbird” issue becomes simple, manageable and stress-free, allowing you to use Thunderbird without interruptions.