2019-0320. My Evolution email client stopped stopped working after my server upgraded Dovecot was from version 2.2 to 2.3. I was getting TLS errors in Evolution. The error was “The reported error was “Failed to get capabilities: Error performing TLS handshake: An unexpected TLS packet was received.” I also have Roundcube webmail based email and it continued to work. The fix to the problem was not hard (Thank you Linux Community) however there is not much information on the internet now on solving this problem and thus the reason I felt motivated to write this post and give back to the Linux community.
My server is Debian Sid (Buster/Debian 10). My email is setup using the guide from https://workaround.org/ispmail/stretch.
The solution to the problem is change the ssl configuration in the dovecot file “/etc/dovecot/conf.d/10-ssl.conf”. I also increased the security of the SSL/TLS protocols used. References are: https://wiki2.dovecot.org/Upgrading/2.3 and https://wiki2.dovecot.org/SSL/DovecotConfiguration.
I first needed to create a new Diffie Hellman parameters file that is involved in the TLS key exchange. This file collects entropy from the computer and took roughly an hour on my slow server computer. Enter these commands in the terminal. https://wiki2.dovecot.org/SSL/DovecotConfiguration#SSL_security_settings
cd /etc/dovecot
openssl dhparam 4096 > dh.pem
I removed the following lines in file “/etc/dovecot/conf.d/10-ssl.conf”.
ssl_protocols = !SSLv2 !SSLv3
I added and modified the following lines in file “/etc/dovecot/conf.d/10-ssl.conf”.
ssl_dh =</etc/dovecot/dh.pem
ssl_min_protocol = TLSv1.2
ssl_cipher_list = ALL:!DH:!kRSA:!SRP:!kDHd:!DSS:!aNULL:!eNULL:!EXPORT:!DES:!3DES:!MD5:!PSK:!RC4:!ADH:!LOW@STRENGTH
ssl_prefer_server_ciphers = yes
Restart the dovecot service
sudo systemctl restart dovecot
Check that the dovecot service is running
sudo systemctl status dovecot
All done and Evolution email is working.