The error message sending of the message failed Thunderbird is one of the most common issues users face when trying to send emails through the Mozilla Thunderbird client. This problem usually occurs due to incorrect SMTP settings, server authentication errors, blocked ports, or security conflicts. Understanding the reasons behind it helps you troubleshoot the issue efficiently and restore smooth email communication.
When Thunderbird cannot send outgoing emails, the first area to check is your SMTP configuration. Every email provider requires specific outgoing server details. If the host name, port, encryption method, or authentication option is incorrect, Thunderbird cannot connect to the mail server. This triggers the sending of the message failed Thunderbird error and may repeatedly interrupt your workflow.
To fix this, open Thunderbird and go to Account Settings. Under Outgoing Server (SMTP), verify that the server address matches your email provider. For example, Gmail uses smtp.gmail.com while Outlook uses smtp.office365.com. Make sure the port is accurate, typically 587 for STARTTLS or 465 for SSL/TLS. Authentication should be set to Normal Password unless your provider specifies otherwise. Saving these correct values helps restore successful email delivery.
Another factor causing sending errors is password authentication. If your password was recently updated or if two-factor authentication is active, Thunderbird may fail to recognize the credentials. In such cases, using an app-specific password becomes necessary. Without correct authentication, the mail server rejects outgoing requests and Thunderbird displays the sending of the message failed Thunderbird notification.
Internet service providers and network administrators sometimes block outbound ports for security reasons. Ports like 25 or 587 may be restricted on certain networks, preventing Thunderbird from communicating with the SMTP server. Switching to a different port recommended by your provider or connecting through a different network can solve this challenge.
Antivirus software and firewalls may also interfere with outgoing email communication. They sometimes block encrypted connections or flag Thunderbird’s SMTP activity as suspicious. To fix this, add Thunderbird to the firewall exceptions list and allow its connection through your antivirus settings. Restarting your system afterward often resolves the issue.
Thunderbird profile corruption is another common cause of sending errors. Over time, folders, settings, or configuration files may become damaged, preventing messages from sending correctly. Creating a new profile or removing old SMTP entries in Account Settings helps refresh the email structure and fix the issue.
If the problem persists, test sending an email from your provider’s webmail. If it works online but not in Thunderbird, the issue lies in the local settings rather than the email account itself. Resetting the SMTP configuration or re-adding the email account in Thunderbird usually resolves such conflicts.
Regular updates are important for maintaining compatibility with evolving email server protocols. Thunderbird updates include performance enhancements, bug fixes, and stronger security features. Running an outdated version may cause sending of the message failed Thunderbird issues due to outdated encryption compatibility. Updating to the latest version ensures smoother synchronization and fewer errors.
Why does Thunderbird show sending of the message failed?
The error appears due to incorrect SMTP settings, authentication failures, blocked ports, or antivirus/firewall restrictions.
How do I check SMTP settings?
Open Account Settings → Outgoing Server (SMTP) and verify server name, port, encryption, and authentication.
Does Thunderbird need an app password?
Yes, if your provider uses two-factor authentication, Thunderbird must use an app-specific password.
Why are my emails stuck in Outbox?
This happens when Thunderbird fails to contact the SMTP server due to incorrect settings or blocked ports.
Can antivirus software block outgoing email?
Yes, antivirus firewalls often block encrypted SMTP connections. Adding Thunderbird to the allowed list fixes this.