==== REQUIRED BASIC INFO OF YOUR IREDMAIL SERVER ====
- iRedMail version (check /etc/iredmail-release): 1.40
- Deployed with iRedMail Easy or the downloadable installer? Installer
- Linux/BSD distribution name and version: CentOS 8.5 and Rocky 8.5
- Store mail accounts in which backend (LDAP/MySQL/PGSQL): MariaDB
- Web server (Apache or Nginx): Nginx
- Manage mail accounts with iRedAdmin-Pro? No
====
Just want to report that our migration from the (now unsupported) CentOS to Rocky 8.5 using Rocky's "migrate2rocky.sh" went flawlessly. See the migration guide.

Instead of taking a full mid-day backup (there are overnight ones anyway), I took a VM checkpoint which would allow quick rollback if it all went belly-up. And I turned off all incoming traffic at the firewall.

It took about 1.5 hours though, and with incoming traffic blocked, the users saw it as down. I suspect it would have been fine if I had kept it handling mail; Linux is really remarkable in its ability to "rebuild the aeroplane in mid-flight".