Hi Nigel
I'm using mailto:
<a href="mailto:sender@sender-domain.com?subject=unsubscribe %email% %group%">Unsubscribe from future emails</A>
Subject line for resulting email is (email changed but group name left as is):
unsubscribe recipient@recipient-domain.com Groups_mailing_list_enta,Groups_mailing_list_goldmine
Using MLK 6.28R