Firewall/NAT

I am wanting to allow email to come from a select server (MXLogic) only to prevent attacks on our exchange server being used as a relay server. I am not sure how to set this up. I have been given the ip address for example 206.60.140.0/21 and  206.60.140.0/24. I don't know if I use Network or single IP/ alias. I also want to use a non-standard port for smtp to make it a bit harder for a bot to find it.

Specifics on this setup would be appreciated.

Thanks.

Use inbound NAT, with auto add firewall rule. Then edit the firewall rule and allow from one of the source networks. Then add a rule based on that rule, with the second source network.

You can use an alternate port for the inbound NAT, though with the restrictive firewall rules that's pretty pointless.

Thanks. I'm still a bit confused on single vs. network in order to get in the right subnet--- but let me give it a try.

Thanks

Can someone tell me in detailed steps how I do this?

I have a RAID-controller on ip: 172.16.150.41 that is trying to send email thru port 25.
My ISP blocks port 25, and my SMTP-host has an alternative port on 2525. How do I redirect port 25 to port 2525 only for my raid-controller?

Please ad screenshots, I'm a n00b.