SMTP Error (-1): Connection to server failed in Webmail (Roundcube)

[KamalG]

I am using Plesk 12.0.18, Centos 6, Postfix, Roundcube

Whenever I try to send email from roundcube webmail I receive the following error

An error occurred!
close
SMTP Error (-1): Connection to server failed.

[root@server postfix]# service postfix restart
Shutting down postfix:                                     [FAILED]
Starting postfix:                                          [  OK  ]
[root@server postfix]# tail -f /var/log/maillog
Aug  6 10:20:51 server courier-pop3s: Connection, ip=[::ffff:127.0.0.1]
Aug  6 10:20:51 server courier-pop3s: LOGOUT, ip=[::ffff:127.0.0.1]
Aug  6 10:20:51 server courier-pop3s: Disconnected, ip=[::ffff:127.0.0.1]
Aug  6 10:21:31 server postfix/postfix-script[27667]: fatal: the Postfix mail system is not running
Aug  6 10:21:31 server postfix/postfix-script[27732]: warning: not set-gid or not owner+group+world executable: /usr/sbin/postdrop
Aug  6 10:21:31 server postfix/postfix-script[27738]: starting the Postfix mail system
Aug  6 10:21:31 server postfix/master[27739]: fatal: bind 0.0.0.0 port 25: Address already in use
Aug  6 10:21:32 server courier-imapd: Connection, ip=[::ffff:127.0.0.1]
Aug  6 10:21:32 server courier-imapd: LOGIN, user=admin@domain.com, ip=[::ffff:127.0.0.1], port=[39092], protocol=IMAP
Aug  6 10:21:32 server courier-imapd: LOGOUT, user=admin@domain.com, ip=[::ffff:127.0.0.1], headers=0, body=0, rcvd=52, sent=156, time=0

postfix check
postfix/postfix-script: warning: not set-gid or not owner+group+world executable: /usr/sbin/postdrop

Kindly Help !!

 

[KamalG]

I also have problems in DNS, after the server reboots the DNS doesn't work properly until I restart the bind service manually..