Starting With Mozilla Thunderbird 10 and newer (and up to at least Thunderbird 17), SSL/TLS protocol failures are no longer user discoverable.

In Mozilla Thunderbird 9 and earlier, if the SSL/TLS protocol handshake with a server resulted in a fatal failure, an error prompt was shown that notified the user about the failure. With Thunderbird 10 and newer, no feedback will be shown, and the user cannot know whether the failure is on the client side or on the failure side, and what exactly causes the problem. With Thunderbird 17, you can at least find the error message hidden in the "error console" that can be opened from the menu (hidden between all the other frequent messages that are dumped to that place).

One example scenario where you'd run into this silent failing is a typical enterprise configuration, where the server requires the client to authenticate with a client certificate. If the client certificate is not accepted by the server, or no such cert hat been installed yet, then Thunderbird will fail silently. (There are additional SSL/TLS protocol failure scenarios where you'll get the same silent failing.)

The reason for this regression is that error reporting was removed, instead of working on a smarter solution for Bug 682329 . All proposals that would have kept the error reporting in Thunderbird working and that could have been implemented by me with a reasonable amount of work were rejected.

In case you'd like to test the regression yourself, you can follow the steps below.

Use Thunderbird to configure an additional email account. When asked by Thunderbird 17 choose existing account.

- Username: test
- email: test@ssltls.de
- password: test (it's wrong, but it doesn't matter)
- check "remember password"
- click continue
- click "manual config"

- Select IMAP
- hostname ssltls.de (NO leading dot as proposed, in other words, NOT .ssltls.de)
- port 993
- SSL/TLS
- auth: normal password

SMTP configuration doesn't matter, you won't be able to send email through this configuration, but in order to allow you to complete the configuration:
- SMTP
- hostname: ssltls.de
- port 465
- SSL/TLS
- auth: normal password

click ok

With thunderbird 17, the test fails, click "advanced config", and in the next dialog click ok.

You'll now see the standard Thunderbird window, and you should have the test account configured. Click on the inbox. Your statusbar (lower part of the window) might show "connected to ssltls" but that's all you'll ever get with Thunderbird 10 and newer, even if you click the "get mail" toolbar button. You might eventually, much later, see a "connection timed out" notification popup, but that's incorrect, and it's not helpful in diagnosing the cause of the problem.

If you do the above with Thunderbird 9 and earlier, you'll get
"An error occurred during a connection to ssltls.de, SSL peer was unable to negotiate an acceptable set of security parameters. ssl_error_handshake_failure_alert"

With Thunderbird 17, this message can be found in the error console.