We were experiencing the following error with Roundcube:
Unexpected condition from IMAP server, closed or corrupt connection to IMAP. Possible mailbox corruption.
Even the IMAP service on the server is running good but still facing the above error.
The cause of this error is “ioncube” is not enabled on the server.
To sort this error you can do the following:
Login to WHM >> Main >> Server Configuration >> Tweak Settings >> PHP >> Select ioncube
Now try to access the emails with Roundcube.You should not face any errors now.
Previously we have discuss about “Session invalid or expired” error that can also be helpful.