At present all of our email goes through external spam filters before delivery to us. So I know the 3 possible ip addresses that will connect to our server to deliver emails.
We have a new requirement for SSL verified email from a few clients. I am adding a new sub-domain MX record for these people to allow them to send email directly to us.
What I want to do is to limit incoming connections on port 25 to a known list of senders - either by IP address or domain name - whichever is easiest and most efficient to manage.
What is the best way to go about this ?
Is there a Postfix lookup I can setup ?
Or should I use iptables ?
Or something different ?
Thanks in advance.