==== REQUIRED BASIC INFO OF YOUR IREDMAIL SERVER ====
- iRedMail version (check /etc/iredmail-release): 1.7.4
- Deployed with iRedMail Easy or the downloadable installer? downloadable installer
- Linux/BSD distribution name and version: Rocky 10.1
- Store mail accounts in which backend (LDAP/MySQL/PGSQL): MariaDB
- 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 a failover Internet connection on my router.  It also has a static IP.  The only issue is I can't get a PTR record created, so I was thinking that perhaps I could use it for incoming mail if there's an issue with the primary and just avoid using it for outgoing email since the PTR record wouldn't match and there's a high probability it would be rejected due to that.

Intead of doing tricks with DNS resolution I was wondering if instead I could designate the failover IP as a lower priority MX record so the incoming mail would still arrive.  Would that cause any issues?

For example I'd have:

main.com  3600 IN MX 10 mail.main.com
main.com. 3600 IN MX 20 failover.main.com