Ah, here's a little bit of progress. I gave ownership of vchkpw to root:vchkpw, and setuid on it:
%chown root:vchkpw /home/vpopmail/bin/vchkpw %chmod 4711 /home/vpopmail/bin/vchkpw Now I authenticate while using SMTP-AUTH... which is great, since it's more secure than the roaming users thing. Unfortunately, I still get the error about the recipient not being listed in rcpthosts: "553 sorry, that domain isn't in my list of allowed rcpthosts." !DSPAM:4af9526a32711762921135!