After upgrading of my e-mailbox running courier-imap-ssl, I discovered that connecting with Thunderbird just failed.
imapd-ssl: couriertls: accept: error:14094417:SSL routines:SSL3_READ_BYTES:sslv3 alert illegal parameter
In Thunderbird, pressing
CTRL+SHIFT+J shows the Thunderbird error console. It showed me information that something was wrong with some DH-parameter.
Following: https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=787579, I generated a new keyfile using:
# export DH_BITS=2048 && mkdhparams
After generating a new “/etc/courier/dhparams.pem” and restarting courier-ssl by executing: /etc/init.d/courier-imap-ssl restart, I still could not connect with Thunderbird…
Then I discovered that in: /etc/courier/imapd-ssl, the parameter TLS_DHPARAMS could be set. I suspected that the pem-file for some reason could not be found by courier-imap-ssl. A bit strange of course, because it had never been a problem, until now.
So I added:
After restarting courier-imap-ssl once again I discovered that this addition indeed solved my problem.
For future convenience I changed the BITS value in /usr/sbin/mkdhparams