Postfix and virtual domains

I'm aware of the fact that the Virtualmin developers are not convinced that there is any benefit in supporting virtual domains for Postfix. However, I'd like to re-start the discussion with a point that might not have been raised before.

I've recently switched a Virtualmin server using Qmail/VPOPMail to Postfix. While I know Qmail/VPOPMail much better than Postfix, I did like the idea of going with the Virtualmin defaults.

I am now faced with the problem that a switch like the one I made on this server entails a change of login. As VPOPMail is a virtual domain system, email addresses are used as logins. Converting them to system accounts does not only change those logins but even changes them somewhat unpredictably. If e.g. I have a domain name example.com and another subserver example.net, one would result in user names like foobar.example and the other one in foobar.example-net (or foobar.example-com depending on which one was created first).

Now, the advantage I see with virtual domains is that they can be kept transparent. I can change what is under the hood without having to bother the users with a change to their software. Using email addresses as logins, I could also easily predict the credentials for users and generate e.g. a document containing those credentials on a computer different from my Virtualmin server without needing to know anything of what Virtualmin did.

I realise that querying a database is unnecessary for most mail setups. However, the database server is running, anyway, and I can't see any harm in using it for virtual mail domains if it adds convenience.