How to get rid of these Postfix warnings

how I interpret the entry is that you can remove the domain listing from mydestination

Sorry, im not a mindreader yet :p
That would be in postfix configuration file.

webmin - servers - postfix mail server - Edit Config Files and look for the $mydestination line. If your domain is listed in there you can remove it and reload or restart postfix.
/etc/init.d/postfix restart

Note that this can get a little bit tricky, if the system hostname exactly matches one of your virtually hosted domains. It will confuse Postfix to remove the hostname from mydestination, because Postfix process the virtual maps before the delivery stage, and so when it gets to the end and it tries to deliver to "name@hostname" it'll fail if it's not in mydestination.

So...simpler to name your server something other than the bare domain name. So, I'd name my system, say "ns0.virtualmin.com" or "srv1.virtualmin.com" or similar, instead of "virtualmin.com". There are ways to deal with this within Postfix, but I never seem to get it right. ;-)

Oh, yeah, also note that this error is harmless.

Excuse me, folks.
I wouldn't be updating this thread, except that I get that rewirte warning too.
It might be harmles, but I'd prefer not to see it.
My mydestination line (after I tinkered about to try to make it work) reads:
mydestination = $myhostname, localhost.$mydomain, localhost, $mydomain

Should it just contain something like mydestination = $myhostname?
Or just:
mydestination =
?
Thanks.

After edit main,cf any entry for domain listas.biomanantial.com

Restart postfix... but problem persist