STARTTLS Handshake problem introduced in 1:31.8.0+build1

[Fionn]

I am running trusty. After the update from 1:31.7.0+build1 to 1:31.8.0+build1 i suddenly was no longer able to send mail via my provider.
The mail server is running exim and uses STARTTLS for connection encryption. When hitting the send button, Thunderbird informed me that it is connecting to the mail server, immediately followed by a popup informing me that sending failed due to an "unknown error" and that I should talk to my network admin.

I then made sure they had not changed anything in the exim server config (for quite some time actually). When I tried to send mail, the server would just have an entry in its log like this:

2015-08-30 15:35:04 TLS error on connection from (my.host.some.where) [176.198.xxx.yyy] (gnutls_handshake): A TLS packet with unexpected length was received.

Sending mail from Android or with Evolution still works.

I then grabbed a backup and downgraded thunderbird to the previous version 1:31.7.0+build1. The problem went away immediately.

A simple test using

#> openssl s_client -connect mail.my.provider.com:25 -starttls smtp

does not exhibit anything uncommon, the handshake goes through without a hickup.

Since thunderbird is not totally uncommon (although noone else seems to have complained yet), I could arrange a test login for anyone willing to run an investigation on the issue. I just don't want to publish server names or IPs here.

[gf (gf-interlinks-deactivatedaccount)]

Hello Fionn,
Thank you for submitting this bug and reporting a problem with Thunderbird. You made this bug report in 2015 and there have been several versions of Ubuntu and Thunderbird since then.

Could you confirm that this is no longer a problem and that we can close the ticket?
If it is still a problem, are you still interested in finding a solution to this bug?
If you are, could you run the following (only once):
apport-collect BUGNUMBER
and upload the updated logs and and any other logs that are relevant for this particular issue.

Thank you again for helping make Ubuntu and Thunderbird better.
G

[Launchpad Janitor (janitor)]

[Expired for thunderbird (Ubuntu) because there has been no activity for 60 days.]