This is going to be a very short post. I faced this issue on a Plesk server. All of a sudden ( it was after a reboot ), Roundcube stopped working. No matter what you do, this is the error you get
Connection to storage server failed
Not very helpful, I know. This is a generic error, there could be a 100 reason why it happens. But, if this happened all of a sudden, then it must be easy to fix.
Make sure that dovecot is running
If it isn’t, restart it
Yeah, I know, the classic, “did you try restarting the service?” It could help someone. But the actual issue I faced was “SELinux”. Every freaking time. :D
Set SELinux to “Permissive”
This was the real culprit in my case. I guess SELinux wasn’t configured properly for roundcube.
This will set SELinux to Permissive. This should fix the issue, in most cases. If it does not, then, well, dig deep. Have fun :D