"M=Mail / T=Transport / A=Agent / C=Client. sendmail, postfix are MTAs and kmail, thunderbird are MTCs. You configure your MTC to use your in/outbound ISP's MTA to receive/send email. If you want to send/receive email among your LAN machines, then you need to configure your MTA on your machines."

I didn't use this for Sandbox, but I'm keeping it just in case.

I didn't use this for Sandbox, but I'm keeping it just in case.

I didn't use this for Sandbox, but I'm keeping it just in case.

I didn't use this for Sandbox, but I'm keeping it just in case.

"If you want to use the PHP function mail() for sending emails to your own email address (like mail@johndoe.com) you just need to open MAMP PRO, go to Server -> Postfix and add the value "johndoe.com" (without quotes and the according domain name) into the field "Domain of outgoing mail"."

Add the following line in /etc/aliases:
user: | "/usr/bin/script.php"

Don't forget to run the following commands afterwards:

$ sudo newaliases
$ sudo postfix reload.

"This article describes how to install a postfix mail server with no extras or optimization. It's intended only for users who are experienced administrators or who just want a basic mail server installed for a single purpose like sending email alerts from another service."