Hi Rob, Michael,
At this stage I am experimenting with iRedMail, the version that uses the MYSQL, back end, and with that version a multi-domain environment is easy to setup, with the exception of the global/domain address book, hence why I have developed a mysql table called contacts in the sogo database and a few db triggers to add/edit/deleted the contacts table when modification/addtions/deletions are done via the iRedMail admin panel, and that work well, now just need to create a couple of php pages on for the admin and one for the users to be able to edit their details.
Having said that, I willl now try the ldap version of iRedMail, and based on the demo ( [Online Demo of the iRedAdmin-Pro (https://www.iredmail.org/admin_demo.html or https://demo-ldap.iredmail.org/) it does support multi-domain environment with user id segregation, once I ahve set that up I will let you know how I go.
As with Nethserver I was not aware of the 'PHPLDAPadmin from stephdl or MS-RSAT " tools.
I have since deleted my Nethserver, but I can always reinstall ( i have an esxi server) and test them again. The only problem that I might be facing is the public IP address as we only have on, so directing port 25 to the mail server is going to be an issue, multiple servers might be able to send out email, but receiving them might be an issue, open to ideas/suggestion on this one.
Hence a single server with a multi-domain configuration resolves the issue.
But will let you know hoe I get on with both a new installtion of Nethserver and iRedMail ldap version.