[Pkg-exim4-users] New Thunderbird incompatible with Jessie courier-imap

[Nick Guerette]

Not about exim, but likely of critical interest to many running a debian 
mail server: libnss 3.19.1 does not accept Diffie-Hellman keys smaller 
than 1024 bits, and in its default configuration on Jessie the common 
courier-imap server uses a 768-bit key.  This means the latest release 
of Mozilla Thunderbird will fail to make secure IMAP connections.

The solution is to change the default key size in the 
/usr/sbin/mkdhparams script from 768 to 2048 and run it.  If 
/etc/courier/dhparams.pem was created less than 25 days ago, the script 
will not update it, so you must first use touch -d to make it older, or 
stop courier and delete dhparams.pem if your operational needs allow.

The bug: https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=787579

The justification for this breakage in a minor version release: 
https://weakdh.org/

Nick Guerette
Embedded Systems Engineer
Mosaic Industries, Inc.
510-790-8222
http://mosaic-industries.com/embedded-systems