All is now working perfectly, after making the following changes:
Removed drop_solo_alias router
In virtual_aliases_nostar router: removed unseen
In virtual_aliases router: added unseen
Cleaned up the RCPT acl rules.
Latest conf file attached.
I have tested with aliases of the form:
localuser: localuser
alias: localuser
alias: localuser1, localuser2, localuser3
It works for all three cases, and rejects unknowns. I think I can now
safely migrate my archived imap-accessed database to the Webmin system
without a hitch. (Same alias files, same users, etc..)
I hope my struggles will at least help someone else. Sorry to waste
anyone else's time.
Phil