I'm moving from sendmail to postfix, but as I am unfamiliar with postfix, I'd like to know if it is possible to do this sendmail scenario in postfix somehow:
In sendmail's /etc/mail/relay-domains I've specified which IP addresses that have the right to send mail through the server.
In postfix I cannot figure out how to achieve the same. I know how to limit it to not allow email for domains not handled by postfix. Though, this mean that anyone can open up a contact to my mailserver with any email client software (for example Thunderbird) and send an email to any of the domains postfix handles. I've come to understand this is default behaviour for Postfix, but surely it has to be possible to limit this function somehow.
The server is running Centos 6.3 with postfix-2.6.6-2.2.el6_1.
I'd really appreciate some help in sorting this out