转载自：http://mabblog.com/blog/2011/09/lion-smtp-postfix-relay-and-dreamhost/
When developing web-apps locally it is useful to have a fully functional smtp server to test automated emails associated with your application. Many times the network you are developing on will not allow you to simply start up postfix and and run your own local smtp server. However, this doesn’t imply that you can’t use postfix – modifying postfix to relay all outgoing mail to an external / offsite smtp server that you have control of will enable you to develop & test the parts of your application that require a local outgoing smtp server without an issue.
Many times port 25 (the default smtp port) will be blocked somewhere along the line in your network connection. You can figure out if your network configuration or ISP is blocking port 25 by running
Edit /etc/postfix/main.cf
smtp_sasl_auth_enable = yes
smtp_sasl_password_maps = hash:/etc/postfix/sasl_passwd
smtp_sasl_security_options = noanonymous
smtp_use_tls = yes
Create/edit /etc/postfix/sasl_passwd
Run this command in your shell once the above two files are created/modified:
sudo postmap /etc/postfix/sasl_passwd
sudo launchctl stop org.postfix.master
sudo launchctl start org.postfix.master
# test postfix, cmd+d after typing message content to send message
mail -s "Testing, Testing" you@domain.com