Great work, thanks to all involved!

I updated our roundcubemail to 1.6 as we are on Ubuntu 20.02 and have PHP 7.4. However, after doing the upgrade users could not log in. I revered to our 1.5.2 backup and it worked fine.

I know this is an issue to resolve with roundcubemail, but I wanted to point it out here to others to be sure to have a good backup of your roundcubemail folder (/opt/www/roundcubemail for us) in case you need it.

I found a workaround, but TBH not sure what the ramifications are.  I changed /opt/www/roundcubemail/config/config.inc.php this setting from false to true.

// Automatically register user in Roundcube database on successful (IMAP) logon.
// Set to false if only registered users should be allowed to the webmail.
// Note: If disabled you have to create records in Roundcube users table by yourself.
// Note: Roundcube does not manage/create users on a mail server.
$config['auto_create_user'] = true;

Update: Re-tagged iRedMail-1.6.1 with OpenBSD 7.1 support, no changes to other linux distributions.
Download here: https://www.iredmail.org/download.html

Yes. And we clearly put this change under "For PostgreSQL backend" section.

Notes on installing iRedMail 1.6.1 on Rocky 9

Enable the CRB repo. (crb enable)
epel 9 is missing two packages but you can build the fedora 35 source rpms available at the below locations. I created a local repo and added it to dnf.

src.fedoraproject.org dovecot-fts-xapian
src.fedoraproject.org python-webpy

I copied the iredadmin rc_scripts/uwsgi/rhel8.ini to rhel9.ini.
I copied the iredadmin rc_scripts/systemd/rhel8.service to rhel9.service and updated the uwsgi path to /sbin/uwsgi and update the conf to rhel9.ini

You may have to install them manually.

I had to manually install fail2ban before running iRedAdmin.sh
I had to run iRedAdmin.sh twice and disable the iRedAdmin dnf repo between them since there isn't a (RHEL/Centos/Rocky) 9 directory so it errors trying to reach the repo.