# During the installation, the SSL certificates for IMAP-SSL and POP3-SSL are created with the hostname localhost. To change this to the correct hostname (server1.example.com in this tutorial), delete the certificates...
cd /etc/courier
rm -f /etc/courier/imapd.pem
rm -f /etc/courier/pop3d.pem
# ... and modify the following two files; replace CN=localhost with CN=server1.example.com (you can also modify the other values, if necessary):
vi /etc/courier/imapd.cnf
[...]
CN=server1.example.com
[...]
vi /etc/courier/pop3d.cnf
[...]
CN=server1.example.com
[...]
# Then recreate the certificates...
mkimapdcert
mkpop3dcert
# ... and restart Courier-IMAP-SSL and Courier-POP3-SSL: