I just installed Postfix Enabler to be able to send my emails through a SMTP server on my own powerbook. I didn’t want the hassle to configure the postfix server myself, so I went for a software doing it the Macintosh way.
The default configuration was a little too open for my taste. I want others (that is me on the PC nearby) to use the postfix server only if they know a password. Using the Postfix Enabler configuration tab to setup password authentication still lets anybody on the same subnet send mail without a password.
Bernard Teo (the author of Postfix Enabler) was very helpful and immediately answered my request: enter this line in the Custom Postfix Settings field:
There is only one downside using your own SMTP server: depending on where you are linked to the internet, your IP address might raise suspicion with spam filters, thanks to the many worms using any “available” PC as spam relay.