backup mx with ispconfig and postfix

[the_spy]

Hello,

I'm using the last stable version 2.2.12 of ispconfig, on a stable debian 4 setup with postfix 2.1.5-9

I want to add a domain in my server as a backup MX for a friend, but it seems it's not an option in ispconfig.

so I found that the option "relay_domains = domain.com" is needed in the main.cf file in postfix to make a backup mx for domain.com

first question, will it work correctly with the ispconfig configuration if I add this line ?

and second question, I do not see the text "//// MAKE MANUAL ENTRIES BELOW THIS LINE! ////" at the end of main.cf, so I'm able to change main.cf manually or not ?

Thanks!