I tried what you said and it did not work. No email sent so I looked in my mail log.
Aug 20 07:05:31 dibisutvecklings-mac-mini postfix/master[14138]: daemon started -- version 2.4.3, configuration /etc/postfix
Aug 20 07:05:31 dibisutvecklings-mac-mini postfix/pickup[14139]: 5C6DDC4E64: uid=70 from=<_www>
Aug 20 07:05:31 dibisutvecklings-mac-mini postfix/cleanup[14141]: 5C6DDC4E64: message-id=<20090820050531.5C6DDC4E64@dibisutvecklings-mac-mini.local>
Aug 20 07:05:31 dibisutvecklings-mac-mini postfix/qmgr[14140]: 5C6DDC4E64: from=<_www@dibisutvecklings-mac-mini.local>, size=636, nrcpt=1 (queue active)
Aug 20 07:05:31 dibisutvecklings-mac-mini postfix/smtp[14143]: 5C6DDC4E64: to=<benny@dibis.se>, relay=mx-cluster2.one.com[91.198.169.11]:25, delay=0.37, delays=0.03/0.01/0.28/0.05, dsn=5.1.8, status=bounced (host mx-cluster2.one.com[91.198.169.11] said: 550 5.1.8 <_www@dibisutvecklings-mac-mini.local>: Sender address rejected: Domain not found (in reply to MAIL FROM command))
Aug 20 07:05:31 dibisutvecklings-mac-mini postfix/cleanup[14141]: B2EB3C4E66: message-id=<20090820050531.B2EB3C4E66@dibisutvecklings-mac-mini.local>
Aug 20 07:05:31 dibisutvecklings-mac-mini postfix/qmgr[14140]: B2EB3C4E66: from=<>, size=2765, nrcpt=1 (queue active)
Aug 20 07:05:31 dibisutvecklings-mac-mini postfix/bounce[14144]: 5C6DDC4E64: sender non-delivery notification: B2EB3C4E66
Aug 20 07:05:31 dibisutvecklings-mac-mini postfix/qmgr[14140]: 5C6DDC4E64: removed
Aug 20 07:05:31 dibisutvecklings-mac-mini postfix/local[14145]: B2EB3C4E66: to=<_www@dibisutvecklings-mac-mini.local>, relay=local, delay=0.01, delays=0/0.01/0/0, dsn=2.0.0, status=sent (delivered to mailbox)
Aug 20 07:05:31 dibisutvecklings-mac-mini postfix/local[14145]: warning: service not found: biff/udp
Aug 20 07:05:31 dibisutvecklings-mac-mini postfix/qmgr[14140]: B2EB3C4E66: removed
Aug 20 07:06:31 dibisutvecklings-mac-mini postfix/master[14138]: master exit time has arrived