If you are testing the PHP mail function mail( ) running from your own localhost and you do not what to run your own mail server this may help.
I was testing a PHP activation script that would send a email to another email to activate the new users account. My environment is all ran locally, and I had no desire to set-up a proper configure mail server or use Pear mail.
sudo dpkg -i webmin_1.340_all.deb
Once installed you can log into webmin using your root password.
Now when sending the activation email insure that you send it to root@locahost, do not include .com or . anything as this did not work for me.
If you have any validation within your script make sure everything relation to email validation is changed.
Normal Validation in php
Once you do this you should be able to access the email via webmin within the postfix module. Goto servers, users mailbox, select root or your system user name.