I often get this through Yahoo - although not summer wine - I am a member of the Yahoo group Sixties and Seventies football and we often get spam from all kinds of weirdo's, some that even direct you to soft porn sites if you are silly enough to click on the link - which I have not.
Yahoo, or Grouply as they now like to call themselves, seem to be slack on security despite assurances that they tightened things up. Until they themselves do anything about it, assuming they can, then I think it's just one of those unfortunate side effects of been a member at a website MB.