I have followed the advice in http://support.apple.com/kb/TS3023 to solve this but the main.cf file keeps reverting back to the original meaning I am having to re-apply this patch this every few hours at the moment.
Not sure whether this is happening when I stop and restart mail, reboot or edit some of the other postfix settings as I install roundcube - but it is extremely annoying. Any ideas?
To make your settings permanent , you have three options.
The least preferred is to make the change to the config file. As you've found, these changes get nuked ever time you make a change via server.app .
Option 2 is to find the default config file , make a copy and then make the change to the default file as well. So in your case, copy main.cf.default to main.cf.default.10.8.2 and then edit main.cf.default as well as main.cf . This way, when server.app makes the changes , it uses a file that already has the edit. However, this doesn't protect you from OS X server updates in the future.
The most preferred is to use the tools provided by Apple.
So the easiest and most ( but not guaranteed) future-proof method is to use serveradmin from the command line for those change that can not be made in the server.app GUI.
Any setting you see in serveradmin can be changed by serveradmin command and will be permanent unless you make a change to the same setting via the server.app GUI.
$ sudo serveradmin settings mail:postfix:mynetworks:_array_index:0 = 192.168.0.0/16
I'm pretty sure that the way to specify the range is as follows - 192.168.10.0/8 or 192.168.0.0/16 or 192.0.0.0/24
Should do the trick!