QVCS pop toaster rcpthosts problem

I have recently set up a qmail pop toaster using Konstantin Ryabitsev's qvcs-guide (qvcs-guide.sourceforge.net). Unfortunately, when I send mail to the server, the account that sent the mail to my users receives the following error message:
Message from yahoo.com.
Unable to deliver message to the following address(es).

<joe@mydomain.net>:
000.111.222.333 does not like recipient.
Remote host said: 553 sorry, that domain isn't in my list of allowed
rcpthosts (#5.7.1)
Giving up on 000.111.222.333.

my virtualdomains file has mydomain.net:mydomain_net, so i really do not know why my server would be rejecting the mail.

Interestingly, I can send mail from the accounts on the server, which i take to mean that the smtp relay is working.

any ideas?

the defaultdomain can send and accept mail to and from mail servers other than the one it is on, but the other virtual domains can only send mail to external servers. all of the domains housed on my server send and receive mail from / to each other.
weird. really frustrating.

when sending mail from yahoo, for example, to one of my virtual domains i get:

Message from yahoo.com.
Unable to deliver message to the following address(es).

<joe@vdomain.com>:
Sorry, I couldn't find any host named vdomain.com. (#5.1.2)