I\'m developing a website that will utilize PHP\'s mail() function. I\'m running MAMP Pro (primarily because it has the Postfix feature that is supposed to be useful for sen
You need to set it up for your ISP.
http://documentation.mamp.info/en/mamp-pro/server/postfix
also
http://blog-en.mamp.info/2009/09/how-to-sending-emails-with-mamp-pro.html
Other than that, I agree with the comments. What is your ISP? What is php telling you? Also, read your logfile for postfix and tell us what it says:
http://blog-en.mamp.info/2010/03/how-to-show-postfix-log-file-of-mamp.html