Postfix Tip of the Day!
If you are using postfix to relay mail to another mail server and the mail server’s address is a dynamic ip or switching ip (as larger ISP use for load balancing) then remember to wrap square brackets around the address. This will allow you to use the dynamic address and not need to specify an absolute address that could change (I have been caught out before).
So to save tears use brackets like so in your /etc/postfix/main.cf file:
relayhost = [mail-hub.bigpond.net.au]
Hazzarh!