I have gone with the Mailwasher suggestion, it seems to be starting to help. There is just a slight gap in the defences as there is a danger of spam arriving in the mail server in the moments between the Mailwasher activity and the fetching of mail by the mail browser. I have an idea about this which I may try to suggest to the Mailwasher author though he has probably thought about it and worked out why it won't work.
Rans6...