What's the correctly way to make Postfix run permanently on Lion (not server)

Solution 1:

The following changes worked for me:

1. Remove the following two elements from /System/Library/LaunchDaemons/org.postfix.master.plist:

   <string>-e</string>
   <string>60</string>
   

   This will stop it exiting after 60 seconds.

2. Add the following element as a child of the <dict>...</dict> element in the same plist file:

   <key>KeepAlive</key>
   <true/>
   

3. Reload the file:

   sudo launchctl unload /System/Library/LaunchDaemons/org.postfix.master.plist 
   sudo launchctl load /System/Library/LaunchDaemons/org.postfix.master.plist
   

postfix should now be running as a daemon.

The above works on Mountain Lion, Mavericks, Yosemite and El Capitan. For systems that have System Integrity Protection (El Capitan and later) there are two options:

1. Copying /System/Library/LaunchDaemons/org.postfix.master.plist to /Library/LaunchDaemons/org.postfix.custom.plist, changing org.postfix.master to org.postfix.custom and then unloading and loading as above.
2. Disabling SIP (using csrutil), making the edits and then re-enabling SIP.

Note: With High Sierra and Mojave, the configuration file is com.apple.postfix.master.plist instead of org.postfix.custom.plist.