Can't get SMTP to work, error message about passwd.db is repeated

I just enabled sendmail on my Mac Air. It works. You don't have to buy a Mac OS X server.

Please refer to this URL:
http://www.garron.me/mac/postfix-relay-gmail-mac-os-x-local-smtp.html

if you still have problem, refer to following URL:

https://discussions.apple.com/thread/1521336?start=0&tstart=0

or

http://slashusr.wordpress.com/2012/02/14/enabling-postfix-for-outbound-relay-via-gmail-on-os-x-lion-11/