How to Fix Thunderbird SMTP Server Error



In some point of time, users of Mozilla Thunderbird email client may have encountered issues while sending messages. The main reason for not being able to send a message is connection problems with SMTP Server. SMTP (Simple Mail Transfer Protocol) is part of TCP/IP protocol that moves the email on and across the network, delivering it to right destination inbox. In this article, we will check common problems on how to fix Thunderbird SMTP Server Error.

Techniques to Fix Thunderbird SMTP Server Error

In order to troubleshoot SMTP Server issues in Thunderbird, following points should be verified:

1. Check SMTP outgoing email settings

For checking SMTP Outgoing email settings, we will perform the following actions:

  • Login to the Mozilla Thunderbird account
  • Go to Tools and select Accounts Settings

  • A window will be opened, click on Outgoing Server (SMTP)

  • Check that the settings detail of the mail server is same as provided in
  • In case the user’s mail settings is not found in Mozilla support article, search for SMTP mail settings on internet for that mail provider
  • Verify that the user’s Thunderbird settings match the documented settings.

2. Ensure that correct SMTP is being used

It is necessary to verify that the correct SMTP is being used for successful delivery of a message. We can check by performing steps below:

  • Go to Tools again and select Account settings.
  • Click on the email address and check the username & email address
  • Make sure that the user is using the correct SMTP server for the email address.

  • Note: One cannot send message from an account provider using different account provider’s service. E.g., you cannot send mail from using Gmail’s SMTP server.

3. Check if the outgoing email is not blocked

The Outgoing email should not be blocked in any way by Firewall, antivirus application or Internet Service Provider. To ensure this, we can check the following:

  • Turn off both the Antivirus as well as Firewall, send the test message and again, send the message by turning on the antivirus and Firewall.
  • Usually, ISP block the outgoing email on port 25 and user can switch to another port like 465 or 587. Contact ISP support to verify if they are not blocking the outgoing email port.

4. Delete the password of SMTP

If any of the above options does not make the user send the message from their Thunderbird account, user can delete the password for that email account by following steps below:

  • Go to Tools → Options in a Thunderbird account

  • Click on Security and select Passwords section

  • Delete the password assigned earlier

5. Set a new password for SMTP

After deleting the password, user can re-set the new password for the SMTP. This is done using ‘Reset email password’ form on the ISP support website.

6. Other Alternatives

If the problem persists, create a new support request providing all the details like screenshots of SMTP settings, mail provider information, ISP, etc. Information such as firewall version being used, Antivirus software with version, OS on which user is working, Thunderbird version can be submitted to ask for solution.


Most of the users of Thunderbird account have encountered problems when their email messages are not being sent to the desired recipient. It is mainly because of SMTP Server issues. The article has discussed various points that will check the common problems related to SMTP error. Any user can refer this article if they ever wonder ‘How to fix Thunderbird SMTP Server error’ with the steps given and can check File Converter.