[CentOS] Linux hosts file /etc/hosts

Good afternoon Gentlemen,

I have a question regarding /etc/hosts for CentOS 6 x64. I already have a hostname set on my server, however there are 10 additional IP aliases assigned to the box, one which I plan to use as a mail server. The mail server will be serving mail for a completely different domain (different then the default hostname of my box). My question is this: If I take one of my additional IP addresses and bind it to postfix for mail, do I also have to specify the remote IP and mail server hostname in /etc/hosts?

For example my hosts looks something like this 127.0.0.1 localhost

Can I add? 66.x.x.x mail.foo.bar

Is this even necessary?