Roundcube error: “Cannot connect to managesieve server” (managesieve is running)

[Wouter_Hamelink]

Hi,

I’m having an issue with Roundcube on my DirectAdmin server.
Roundcube keeps showing the error:

“Cannot connect to the managesieve server”

This happens specifically when I go to Settings → Filters in Roundcube.

What I have already checked:

- Dovecot is running normally
- Managesieve is enabled in /etc/dovecot/conf/protocols.conf:
protocols = imap pop3 lmtp sieve

- The managesieve listener is active on port 4190:
ss -tulpn | grep 4190
Both IPv4 and IPv6 listeners are present.

- Telnet to the managesieve service works:
telnet localhost 4190
I receive the correct Dovecot Pigeonhole capabilities.

- The Roundcube plugin is enabled:
$config['plugins'] = ['managesieve','password','archive','zipdownload'];



- Apache and PHP-FPM restarted
- Full server reboot

Problem:

Roundcube still shows the same error when opening Settings → Filters, even though managesieve is reachable and responding via telnet.