==== REQUIRED BASIC INFO OF YOUR IREDMAIL SERVER ====
- iRedMail version (check /etc/iredmail-release): 1.7.4 MARIADB edition.
- Deployed with iRedMail Easy or the downloadable installer? downloadable installer
- Linux/BSD distribution name and version: Rocky Linux 10
- Store mail accounts in which backend (LDAP/MySQL/PGSQL): MySQL
- Web server (Apache or Nginx): NGINX
- Manage mail accounts with iRedAdmin-Pro? No
- [IMPORTANT] Related original log or error message is required if you're experiencing an issue.
====
I have finally gotten my old server running CentOS 7 upgraded to 1.7.4 and have built a new server running Rocky Linux 10 and installed a fresh iRedMail 1.7.4 install.  I've made the customizations needed except for one, allowing my backup MX servers access.

On the old server in main.cf I had:

smtpd_client_restrictions = permit_mynetworks, permit_sasl_authenticated, check_client_access hash:/etc/postfix/client_access, reject_unknown_client_hostname

And /etc/postfix/client_access contained:
mx1.backupmx.com   OK
mx2.backupmx.com   OK
mx3.backupmx.com   OK
xxx.xxx.xxx.xxx         OK

The first three are my backup MX server FQDNs (domain changed in the example) and xxx.xxx.xxx.xxx is the IP of a security scanner that has access.

On the fresh 1.7.4 install smtpd_client_restrictions isn't defined in main.cf so I'm guessing there's a different way I should be doing this.  If I'm understanding the Postfix documentation if smtpd_client_restrictions isn't defined all incoming connections should be allowed and I wouldn't need to do anything but I want to verify before I do the final cutover.