Connection dropped by IMAP server : When you are trying to login to your email account in Roundcube Webmail client(cPanel).
You can try to fix the issue by following the steps below:
If you are using Roundecube check the following logs :
#tail -50 /var/cpanel/roundcube/log/errors
1. Try to restart the IMAP service
# /etc/init.d/courier-imap restart
2. Try to update the courier imap server
#/scripts/courierup –force
3. If the issue still not solve, run the command below to fix the permission for mail directory
# chown -R user:mail /home/user/mail