Issue:
Users of Roundcube webmail report the following error message displayed when attempting to access a folder in webmail:
An error occurred! Server error! (OK)
Access the Roundcube error log at:
/var/cpanel/roundcube/log/errors
and the following error entry will possibly be displayed:
Unexpected condition from IMAP server, closed or corrupt connection to IMAP. Possible mailbox corruption.
As stated, the above error message indicates a potentially corrupt index file.
Solution:
The basic idea behind Dovecot’s index files is that it makes reading the mailboxes a lot faster. Each mailbox has its own separate index files. If index files are missing, Dovecot creates them automatically when the mailbox is opened. Thus, establish an SSH session with the server and navigate to:
/home/<username>/mail/<domain name>/<email account name>/
Find dovecot.index and rename it to dovecot.index.bak
Note: Quite possibly it may be necessary to complete this activity in other folders, specific to the account (such as .Trash, .Sent, etc).
Log the webmail user back into Roundcube webmail and the error should no longer appear (as a new dovecot.index file is generated upon login).
If this does not work try restarting dovecot. Wait a few seconds and then relogin into webmail. Should be working
This article is thanks to ServerSupport
