One-stop resource on how to effectively disable SSLv3 in major web browsers as well as in web, mail and other servers that may still be using it.
Put the following line in your /etc/courier/imapd-ssl configuration file, or modify existing:
IMAPDSSLSTART=NO IMAPDSTARTTLS=YES IMAP_TLS_REQUIRED=1 TLS_PROTOCOL=TLS1 TLS_STARTTLS_PROTOCOL=TLS1
Then restart the server (in Ubuntu: sudo service courier-imap restart).