How to Fix Thunderbird SMTP Error, Cannot Send Messages Error?

Mike Lucanc | how to | 4 minutes read | Modified on: 27-07-2022

Understand How to Fix Thunderbird SMTP Error, Cannot Send Messages Error?

Thunderbird is an open-source email client that supports users with well-organized management of their messages, emails, newsgroups, newsfeeds, meetings, and chats. Despite the ease and productivity of Thunderbird, one also faces a few communal email glitches due to the failure to open up or unable to send messages. Here, in this blog, we learn how to fix Thunderbird SMTP Error, Cannot Send Messages Error.

What is SMTP Error: Messages Cannot Send?

Occasionally while using the Thunderbird application users have come across issues in sending emails. Thunderbird email not responding or SMTP server error is the leading causing reason for this problem

To send and receive email, SMTP is an internet standard used by mail servers. With the SMTP error, one can know the issue behind the /email wasn’t sent successfully. So that user can check the bounce error message and diagnose the issue of bouncing outgoing and incoming messages.

Possible Solution to Fix the Thunderbird SMTP Server Error: Message Cannot be Sent

If you are facing this problem once in a while then it is fine, but what if you are continually facing the Thunderbird issue, then it’s time to look for a solution.

Option 1 – Check SMTP and IMAP Settings

1 – Login to the Thunderbird application

2 – Click on the Tools option and then Account Settings

3 – Go to the Outgoing Server (SMTP)

4 – Now you have to check if the mail server details are the same as according to the Thunderbird

Start the SMTP mail setting search. Follow the steps to check the SMTP settings

  • Open Thunderbird and go to the Account Settings
  • Check your email address, user name, and password
  • Make sure of using the right SMTP server with the email address

With the help of the above steps, you can check whether you are using the right SMTP or not.

Option 2 – Find Out If Outgoing Email Is Not Blocked

Here you need to verify that your outgoing is not being blocked with antivirus, any firewall, or your internet service provider and antivirus. Follow the mentioned steps-

  1. Try to send a test mail turning off antivirus and firewall. Then turn them on and send another test mail. Like this, you can verify the reason for the error.
  2. Many Internet service providers block outgoing emails on port no 25. You may have to change to another port no like 465 or 587 or contact your ISPs to see if they are blocking the outgoing email port.

Option 3 – Reset SMTP Password

Try deleting SMTP Password

  • Go to the Tools and then click on Options
  • On the options, list click on Security
  • Click on the password option and delete SMTP Password

Now, again configure the account and try to send a test email again; possible this can resolve the email not sending error. Else, just change the SMTP password via ‘reset email password’ from ISP’s provision website.

Option 4 – Update Thunderbird

For TLS encryption protocol, Mozilla Thunderbird 78 is looking for an advanced security standard. In case the latest version of the protocols is not buoyed by the provider, receiving and sending messages may get fail. So, you may have to update the Mozilla Thunderbird to the latest edition.

Solution 5 – Switch to Other Email Application

If the above solution doesn’t work, then we will highly suggest using BitVare MBOX to PST Converter Tool. This helps you to migrate to another email client like Outlook for better-emailing involvement.

Outlook supports managing all your user accounts from one application without login for a new arrangement of services and new user accounts. It can simply connect all your user accounts. It infers those users can easily manage emails, search, and apply other features crossways all accounts without using any intricate filters.

The MBOX to PST tool runs on all Outlook versions 2019, 2013, 2016, and others. One can even migrate all emails of Apple Mail to Outlook PST format with all email accuracy, mailbox structure, properties, and original formatting. With this tool, you can easily perform the Thunderbird Data Migration to Outlook without losing any data.


It can be very annoying to Thunderbird users when the Message Cannot Send error continues. Even though this error simply fixed, some people may like to migrate to the Outlook environment. Some users can migrate to Outlook from Thunderbird by using the MBOX Converter tool. It allows users to convert multiple MBOX files from several email clients for migration and easily migrate all emails with attachments to PST, PDF, MSG, CSV, EML, etc. Even it also works for exporting Thunderbird to Gmail, Microsoft 365,, and many more without causing any trouble to the original email Meta properties. If you are looking for some more Thunderbird troubleshooting support, then stay tuned with us for our upcoming troubleshoot blogs.

If you are in search of more powerful professional yet affordable tools, then you can go through our BitVare official website for more certified software, which supports email backup from 25+ email clients, webmail servers to multiple platforms, and a lot more.