IMAP Error (Connection dropped by IMAP server)

To troubleshoot the IMAP error(Inbox lock errors) while accessing mailbox via any webmail clients(Horde, SquirrelMail, NeoMail, Round Cube etc.):

The error will be shown as below,

Connection dropped by IMAP server

ERROR: Connection dropped by IMAP server.
Query: SELECT INBOX
Reason Given: Unable to open this mailbox.

The error usually occurs when there is inbox.lock file in the mailbox.
Here the inbox gets locked and hence the mailbox can't be accessed and
you will get the above said error.

1. Remove the inbox.lock file from the particular mailbox.

Eventhough the inbox.lock file is deleted, it will be created when
the mailbox is accessed again. Hence after removing the file, we need
to copy the inbox to a new file name so as to fix the issue which can
be done as follows,

2. cat inbox > inbox.new
3. rm inbox
4. mv inbox.new inbox
5. Then fix ownership and permissions.

This fixes the issue.