If you cannot send messages, this page provides a series of steps you can follow to check for common problems. If you have problems receiving messages, see Cannot receive messages.

Verify your SMTP outgoing email settings

• In the Thunderbird menu bar, click the ToolsEdit menu and select Account Settings, or click the Application menu button and select OptionsPreferences and Account Settings from the sub-menu, and select Outgoing Server (SMTP) from the bottom of the list in the left panel. Check that the settings are the same as documented in the article for your mail provider (Gmail, Yahoo, Comcast, Hotmail, Sympatico…) OR
• Look for an SMTP mail settings article on the mail provider's site. This is usually in the support section of their website; searching for “mail settings” or “SMTP” will usually find it. Check that your Thunderbird settings match the documented settings.

Verify the correct SMTP Server is being used

• In the Thunderbird menu bar, click the ToolsEdit menu and select Account Settings, or click the Application menu button and select Account Settings, and select the account name. Verify that you are using the right SMTP server for the email address. Most of the time, you cannot send messages from one account provider using another account provider's service. For example, you cannot send a mail from “[email protected]” through Yahoo's SMTP server.

Verify that your outgoing email is not being blocked

Verify that your outgoing email is not being blocked by your firewall, VPN, proxy, antivirus software (which sometimes implements a proxy and intercepts email) or your Internet Service Provider:

• Try briefly turning both antivirus, VPN, proxy and firewall software off, sending a test email, and turning them on and sending another test email.

• Many ISPs block outgoing email on port 25. You may have to switch to another port (e.g. 587 or 465). Contact your ISP's support to see if they are blocking your outgoing email port.

Verify that your mail server supports the minimum version of TLS

As of version 78, Thunderbird expects higher security standards for the so-called TLS network encryption protocol. If your provider does not support the newer versions of the protocol, sending and receiving of messages may fail. You can temporarily lower the bar to check if this is the reason for your problem (which obviously reduces security, so it's not recommended). More details and instructions here:

Thunderbird 78 FAQ – After upgrading to Thunderbird 78, I cannot get or send email messages

Delete SMTP Password

Try deleting your SMTP password. However, don't do this as a first step, especially if you cannot send messages after updating Thunderbird while you previously could. In such case, usually there is nothing wrong with a stored SMTP password in Thunderbird (see above).

Reset SMTP Password

Try changing your SMTP password. This is usually done via a “reset email password” form on your ISP's support website.

If this list doesn't help

Please create a new support request with a screenshot of your SMTP settings with your user ID obscured, and include the following information: your mail provider (for example, Gmail), ISP (for example, Comcast), firewall version (if any), antivirus software and version (if any), operating system and version (for example, Windows 11 or macOS 14 Sonoma), and Thunderbird version (for example, Thunderbird 115.6.0). For information on how to create a screenshot, see How do I create a screenshot of my problem?

More resources

• MozillaZine's technical but very helpful knowledge base article on this topic
• Thunderbird and antivirus related issues