I find that another DH user can secretly intercept mail from me via DH SMTP to an external domain by creating a bogus DNS entry in the DH mail system. For obvious reasons I won't say precisely how, but the point is it can be done extremely easily, even accidentally.
this was supposed to have been changed already - I think it might have been
accidentally reverted (hard to say as our old DNS/Mail person is no
longer with us but it sounds like it is being taken care of).
so I'm hoping for a fix.