Hi Jocke,
Thanks for your response. I'd be interested in a further response when
you have more time.
In the meantime, there's a post on the Google Postini forum from a
user making use of purpose-built addresses for mailing lists etc.
http://tinyurl.com/y97g398
He has been able to get this to work for him, so it does seem worth pursuing.
Thanks,
Duggie