I just completed configuration of my mail server. I have two linodes, an app server and a mail server. The app server is configured to use the mail server to send out user registration email.

On the mail server I have configured /etc/postfix/main.cf as follows:

mynetworks = 127.0.0.0/8, <app-server-ip>/32

My intention is that mail can originate locally on the mail server and well as from the app-server-ip and only the app-server-ip. I'm just looking for feedback from the experts whether I have done this correctly. I'm not at all familiar with the CIDR notation.

Thanks in advance!

You don't really need the "/32" on the app-server-ip, but it should work fine the way you have specified it.