How to automatically start postfix on boot?

Create a login hook: http://support.apple.com/kb/HT2420

Of, for a few extra clams, MailServe:

http://www.cutedgesystems.com/

This is a really solid product, and I've used it since 10.3 Panther OS, with great success.

By the way, I have no affiliation with this product or company...

I use this, in /Library/LaunchDaemons:

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE plist PUBLIC "-//Apple//DTD PLIST 1.0//EN" "http://www.apple.com/DTDs/PropertyList-1.0.dtd">
<plist version="1.0">
<dict>
 <key>KeepAlive</key>
 <true/>
 <key>Label</key>
 <string>smtp</string>
 <key>ProgramArguments</key>
 <array>
 <string>/usr/libexec/postfix/master</string>
 </array>
</dict>
</plist>

Depending on how you want it to work, you may also need to edit the config files in /etc/postfix.

There is already an org.postfix.master.plist file in /System/Library/LaunchDaemons
I had an old copy of Postfix Enabler from http://cutedgesystems.com/ but didn't appreciate having to buy a new program when Leopard came out, so I rolled my own. Here is my edited org.postfix.master.plist:

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE plist PUBLIC "-//Apple Computer//DTD PLIST 1.0//EN" "http://www.apple.com/DTDs/PropertyList-1.0.dtd">
<plist version="1.0">
<dict>
 <key>Label</key>
 <string>org.postfix.master</string>
 <key>OnDemand</key>
 <false/>
 <key>Program</key>
 <string>/usr/libexec/postfix/master</string>
 <key>ProgramArguments</key>
 <array>
 <string>master</string>
 </array>
 <key>QueueDirectories</key>
 <array>
 <string>/var/spool/postfix/maildrop</string>
 </array>
</dict>
</plist>

This will enable you to send mail. You can setup your Mac to receive mail too, but that is a bit more involved.

Thanks for that. I'll give it a go and see if I can send e-mail to myself. 😉