Hi,
in my server there isn't /var/log/plesk-roundcube/errors and /var/log/psa-horde/psa-horde.log is empty.
Here /var/log/maillog after restart server:
Oct 18 14:28:47 cloudlnx spamd[2139]: logger: removing stderr method
Oct 18 14:28:49 cloudlnx spamd[2142]: spamd: server started on port 783/tcp (running version 3.3.2)
Oct 18 14:28:49 cloudlnx spamd[2142]: spamd: server pid: 2142
Oct 18 14:28:49 cloudlnx spamd[2142]: spamd: server successfully spawned child process, pid 2143
Oct 18 14:28:49 cloudlnx spamd[2142]: spamd: server successfully spawned child process, pid 2144
Oct 18 14:28:49 cloudlnx spamd[2142]: prefork: child states: II
Oct 18 14:28:49 cloudlnx courier-authdaemon: modules="authpsa ", daemons=5
Oct 18 14:28:49 cloudlnx courier-authdaemon: Installing libauthpsa
Oct 18 14:28:49 cloudlnx courier-authdaemon: Installation complete: authpsa
Here I login with Horde
Oct 18 14:29:57 cloudlnx courier-imapd: Connection, ip=[::ffff:127.0.0.1]
Oct 18 14:29:58 cloudlnx courier-imapd: LOGIN, user=myuser@mydomain.com, ip=[::ffff:127.0.0.1], port=[44230], protocol=IMAP
Oct 18 14:29:59 cloudlnx courier-imapd: LOGOUT, user=myuser@mydomain.com, ip=[::ffff:127.0.0.1], headers=0, body=0, rcvd=24, sent=286, time=1, starttls=1
Oct 18 14:30:00 cloudlnx courier-imapd: Connection, ip=[::ffff:127.0.0.1]
Oct 18 14:30:00 cloudlnx courier-imapd: LOGIN, user=myuser@mydomain.com, ip=[::ffff:127.0.0.1], port=[44234], protocol=IMAP
Oct 18 14:30:03 cloudlnx courier-imapd: LOGOUT, user=myuser@mydomain.com, ip=[::ffff:127.0.0.1], headers=0, body=0, rcvd=180, sent=863, time=3, starttls=1
Oct 18 14:30:08 cloudlnx courier-imapd: Connection, ip=[::ffff:127.0.0.1]
Oct 18 14:30:08 cloudlnx courier-imapd: LOGIN, user=myuser@mydomain.com, ip=[::ffff:127.0.0.1], port=[44400], protocol=IMAP
Oct 18 14:30:11 cloudlnx courier-imapd: LOGOUT, user=myuser@mydomain.com, ip=[::ffff:127.0.0.1], headers=40, body=0, rcvd=539, sent=25231, time=3, starttls=1
Oct 18 14:30:21 cloudlnx courier-imapd: Connection, ip=[::ffff:127.0.0.1]
Oct 18 14:30:21 cloudlnx courier-imapd: LOGIN, user=myuser@mydomain.com, ip=[::ffff:127.0.0.1], port=[44452], protocol=IMAP
Oct 18 14:30:22 cloudlnx courier-imapd: LOGOUT, user=myuser@mydomain.com, ip=[::ffff:127.0.0.1], headers=78, body=0, rcvd=250, sent=8413, time=1, starttls=1
Oct 18 14:30:25 cloudlnx courier-imapd: Connection, ip=[::ffff:127.0.0.1]
Oct 18 14:30:25 cloudlnx courier-imapd: LOGIN, user=myuser@mydomain.com, ip=[::ffff:127.0.0.1], port=[44466], protocol=IMAP
Oct 18 14:30:25 cloudlnx courier-imapd: LOGOUT, user=myuser@mydomain.com, ip=[::ffff:127.0.0.1], headers=0, body=568, rcvd=205, sent=1946, time=0, starttls=1
Oct 18 14:30:28 cloudlnx courier-imapd: Connection, ip=[::ffff:127.0.0.1]
Oct 18 14:30:28 cloudlnx courier-imapd: LOGIN, user=myuser@mydomain.com, ip=[::ffff:127.0.0.1], port=[44482], protocol=IMAP
Oct 18 14:30:28 cloudlnx courier-imapd: LOGOUT, user=myuser@mydomain.com, ip=[::ffff:127.0.0.1], headers=0, body=568, rcvd=141, sent=1449, time=0, starttls=1
Here after save parameter on plesk Mail Server Setting --> Server-Wide Mail Settings
Oct 18 14:32:06 cloudlnx postfix/postfix-script[3963]: warning: not set-gid or not owner+group+world executable: /usr/sbin/postdrop
Oct 18 14:32:06 cloudlnx postfix/postfix-script[3970]: starting the Postfix mail system
Oct 18 14:32:06 cloudlnx postfix/master[3972]: daemon started -- version 2.11.5, configuration /etc/postfix
Oct 18 14:32:07 cloudlnx courier-authdaemon: stopping authdaemond children
Oct 18 14:32:07 cloudlnx courier-authdaemon: modules="authpsa ", daemons=5
Oct 18 14:32:07 cloudlnx courier-authdaemon: Installing libauthpsa
Oct 18 14:32:07 cloudlnx courier-authdaemon: Installation complete: authpsa
Oct 18 14:32:14 cloudlnx postfix/postfix-script[4490]: refreshing the Postfix mail system
Oct 18 14:32:14 cloudlnx postfix/master[3972]: reload -- version 2.11.5, configuration /etc/postfix
It seems that Postfix mail system don't start at boot. It's possible ?