Some times this error occurs in cpanel based servers due to some problems related with the IMAP server. It happens when you are trying to login to email account in Roundcube Webmail client.
Error : Connection dropped by IMAP server
You can check the below mentioned log file to find the cause:
To resolve this error:
Step 1: try to find out the IMAP service is running or not.
Restart the IMAP service from command line.
Step 2: Update the courier-imap server.
Then check the issue is stil persisting or not. If it is there, Check the ownerships of ‘mail‘ and ‘etc‘ folders of users and make the permission like follows:
chown -R $USERNAME:mail /home/$USERNAME/mail/ chown -R $USERNAME:mail /home/$USERNAME//etc/
Where $USERNAME is the cPanel user name.
That’s it..This will fix the issue with IMAP