Same, though go with “I use the incoming address name to file things into the right folder, so work things, banking things, shopping, and such, are separated” – I don't butter them up by making them sound important enough that I created a mail inbox just for them.

If they still object then I don't sign up. I've had web form refuse to accept an email address with their company name in, so that sale went elsewhere, and one physical retail store wouldn't let me sign up to their prize draw with such an address, so I didn't. In neither case do I suspect anything of value was lost by myself!