with a little help from my friends, thanks Keef and Tony, I have now three live incoming email addresses. Sending the same message to all three (single circulation list) addresses shows that it is only the ones directed through our original host service that are getting bu99ered.
Since we get the hosting there for free we can't complain too loudly. The techy guy that sorts it for us, normally resident in the UK, is 5 hours east of here (on holiday perhaps) and the response to our issue has been non existent, so far. Ho hum.
Rans6