[vPostMaster] 450 Server Configuration Problem

[Ecomshare]

Greetings,

I've been looking in the logs but can't find out why I'm getting a:
"host mail1.mybox.com[207.XX.XX.XX] said: 450 Server configuration
problem (in reply to RCPT TO command)"

Some mail flows fine, others get stuck at the originating server with
the above as an error. There is nothing in my mail.err file.

Any ideas of where to look for specifics?

Thanks!

Barney