> > > virtual_alias_maps = mysql:/etc/postfix/sql/virtual_alias_maps.cf
> >
> > This is virtual_alias_maps, the thing which REWRITES addresses
> >
> > > Apr 29 15:26:03 example postfix/virtual[17937]: C771D11CC61B:
> > > to=<al...@example.com>, relay=virtual, delay=1, status=bounced
> > > (unknown user: "al...@example.com")
> >
> > THIS is the virtual delivery agent at work, which uses
> > virtual_MAILBOX_maps

The error message is not related to that particular setting. You'll
need to take a closer look at the Virtual Address ReadMe to troubleshoot
your set up. If you grep your main.cf file for "virtual" then you'll
either find virtual *mailbox* settings that conflict with your
virtual *alias* settings or that the ultimate destination for the
aliased address is not configured properly in virtual mailboxes.

Chris