Men writing as women and women writing like men

When we analysed "Atonement", I realized that the story was narrated by a woman, and that the book was written by a men. Then, I decided to search for some authors that did this, I mean, women writing as men and men writing as women.
We have the following men that write like women:
-Daniel Defoe, The Fortunate Mistress
-Samuel Richardson, Pamela
-John Cleland, Memories of a women of pleasure

And the following are women that write like men:
-Charlotte Brontë, The Professor
-Edith Warthon, Ethan Frome
-Agatha Christie, The Murder of Roger Ackroyd

This are a few of the big amount of authors that write in another gender. I think it shooud be very difficult for a man to express his feelings as a woman and make the audience feel that way.