Hi!!
My Firewall is ok.
I migrated the courier to dovecot. The problem persisted.
So I reinstalled Postfix. And the miracle happened!
The roundcube is sending emails normally.
Thanks to all for your help. :D
hi Trialotto!
i did an upgrade from Plesk 17.5.3 to version 17.8.11
error log:
[08-Aug-2018 20:15:08 UTC] ERROR: stream_socket_client(): unable to connect to $
[08-Aug-2018 20:15:08 UTC] ERROR: Failed to connect socket: stream_socket_clien$
[08-Aug-2018 20:15:08 +0000]: <c1hk1r0d> SMTP Error...
I'm having the same problem, after updating Plesk.
I'm using Plesk Onyx 17.8.11 on a Ubuntu 16.04.5 VPS.
Postfix.
After update, when i use roundcube, an error appears: SMTP Error(-1): Connection failed
If I use horde, the email is sent normally.