The emails were all in the Spam folder.  I have uninstalled Spamassassin 
because it was more bother trhan it was worth.  It looks as though I shall 
have to do the same with Bogofilter.

This has only been happening since Friday noon.  Which still leaves 
unanswered, of course, why it started to happen. :-/

Thanks to you all.

Lisi