==== REQUIRED BASIC INFO OF YOUR IREDMAIL SERVER ====
- iRedMail version (check /etc/iredmail-release): 1.1 MARIADB edition
- Deployed with iRedMail Easy or the downloadable installer? Downloadable installer
- Linux/BSD distribution name and version: CentOS 7
- Store mail accounts in which backend (LDAP/MySQL/PGSQL): MARIADB
- Web server (Apache or Nginx): None
- Manage mail accounts with iRedAdmin-Pro? No
- [IMPORTANT] Related original log or error message is required if you're experiencing an issue.
====

I successfully deployed my first iRedMail server accepting mail for multiple domains. Now I'm trying to set up a second one as a backup MX. Ideally I don't want to have to configure any users/aliases on this server but just have it do antispam/virus, accept mail for my domains, and forward to the primary MX.

I installed iRedMail as I did for the first server, added all of my domains to the domain table, and set backup_mx = 1 for all domains.

I did not add any mailboxes, aliases, etc.

However, when I send mail to one of the users I get:
Mar  8 03:30:40 mx2 postfix/pipe[2128]: 48Zn1X0pGSzcs7x: to=<REDACTED>, relay=dovecot, delay=0.11, delays=0.02/0.02/0/0.08, dsn=5.1.1, status=bounced (user unknown)

How can I configure iRedMail to act as a backup MX as described above. Thanks!