==== REQUIRED BASIC INFO OF YOUR IREDMAIL SERVER ====
- iRedMail version (check /etc/iredmail-release): 1.6.7
- Deployed with iRedMail Easy or the downloadable installer? downloadable installer
- Linux/BSD distribution name and version: ubuntu 22.04 server
- Store mail accounts in which backend (LDAP/MySQL/PGSQL): PGSQL
- Web server (Apache or Nginx):nginx
- Manage mail accounts with iRedAdmin-Pro? Not at the moment
- [IMPORTANT] Related original log or error message is required if you're experiencing an issue.
====

We're wanting to send mail from our iredmail source server to a destination domain where we want to use the external IP for the destination domain SMTP server. (ie we want to override this domain only) Our issue is that the 2 domains have an internal interconnection so we are getting the internal host IPs for the destination domain when we do a DNS lookup. I want to override the MX record and the A records for this domain only (and any other records eg TXT) that are required.
My initial thought was to add entries for the A records for the destination domain SMTP server to /etc/hosts. This does not resolve the issue as traffic to the internal destination domain servers is blocked.
I'm looking for some guidance on what to poke at next. Is it the smtp_dns_support_level or trivial_rewrite or  something else?

It is only this destination domain that we are having issues with. We can send mail to other external destinations like gmail.