A little background...
I originally had multiple Wordpress sites. I had one domain and multiple sub-domains setup as a Top-level Server and sub-servers.
I had emails setup in each of the servers:
Top-level server - info@example.com Sub-server1- info@subdomain1.example.com Sub-server2 - info@subdomain2.example.com
I have now converted my multiple Wordpress sites, each with its own server, into one Wordpress Multisite. This means that all sites are part of the Top-level server and through .htaccess redirects and a server alias of *.example.com in Apache, Wordpress determines which site to serve.
So my question is, how do I create the old email accounts for the sub-servers/domains when everything is now in the top-level server?
So you basically need email accounts @ multiple domain names differing from the domain in which they are defined? Hm, I'm not sure if that is even possible in this form.
Even as an "additional email address" Vmin will refuse a subdomain that is not under its management. And aliases always have @example.com as domain name too.
I'm not certain, but I guess to accomplish this, you'll need to manually fiddle with Postfix' virtual domain mapping tables. Which will not suffice though if you want users to be able to log on using that email address and fetch mail.
My suggestion would be to keep the old subdomains active, even if it's only for the email accounts and even though Wordpress is no longer installed there. You might turn off the Apache and DNS feature and stuff, and only keep the Mail feature active. It's sure cleaner this way.