How to Fix: Thunderbird: error 'Peer using unsupported version of security protocol.'

Thunderbird users who are trying to send emails through an old exchange email server may encounter an error message indicating that the peer is using an unsupported version of the security protocol. This issue affects users who have updated Thunderbird to version 78 and are experiencing problems with sending emails to their exchange server.

This error can be frustrating for users who rely on Thunderbird for their email needs, especially if they have already invested time in setting up their account configuration. However, there is a solution available that can help resolve this issue.

💡 Why You Are Getting This Error

• The primary reason why this error occurs is due to the version of the security protocol used by the exchange server not being compatible with Thunderbird's updated version. Specifically, Thunderbird 78 requires a minimum version of the TLS (Transport Layer Security) protocol, which may be outdated on older exchange servers.
• Another possible cause could be the configuration settings related to the exchange server. If the configuration is incorrect or incomplete, it can lead to errors like this one.

🛠️ Step-by-Step Verified Fixes

💡 Conclusion

Resolving this issue requires a combination of updating Thunderbird's TLS version and adjusting the exchange server configuration settings. By following these steps, users can get their emails working again with their old exchange server.