Installing DKIM & SPF
Postfix and opendkim already installed!
Stopping Clam AntiVirus Daemon: [  OK  ]
Starting Clam AntiVirus Daemon: [  OK  ]
Stopping spamd: [  OK  ]
Starting spamd: [  OK  ]
Shutting down Mail Virus Scanner (amavisd): [FAILED]
Starting Mail Virus Scanner (amavisd): [  OK  ]
Stopping Dovecot Imap: [FAILED]
Starting Dovecot Imap: [FAILED]
Shutting down postfix: [  OK  ]
Starting postfix: [  OK  ]
Stopping OpenDKIM Milter: [  OK  ]
Generating default DKIM keys: [WARNING]
Cannot determine host's domain name, so skipping default key generation.
Starting OpenDKIM Milter: [  OK  ]
Cant find what I m doing wrong  

fixed problem with my hostname......