Actually I think I know what the problem is. I don't really want to move to Gmail at all, it's just the thing I'm using at the moment as a workaround for the main problem. And that's that I want mail to me at chiark to just work. That's my published contact address. It has been for a year or two, since I finally decided to retire the lspace one. I don't want to have to change it again.
I guess that means trying to work out how the hell SAUCE works so I can write a patch for it to hopefully make the hotmail problem become a thing which is ignored by those who (like me) have configured their address to be checked in lax mode, where it only warns about things rather than rejecting mail.
And think about the official address change for the future. Whether it's to go back to a forwarding address which I can move around with supplier, or to make eleanorb@slimy be my official one and possibly have the same problem again in the future.