These are satire.
However, the camaraderie back and forth that is so great in these letters, existed between CS Lewis and Tolkien. Although later in their lives there was some strife.
JRR Tolkien and CS Lewis were part of a literary society called the Inklings. There is a book about this group which shares the impact of their friendship. It is a great read and it was interesting to me how harsh they critiqued each other's work.
CS Lewis and Tolkien's friendship outside the Inklings is also a very cool story. http://www.christianitytoday.com/history/2008/august/j-r-r-tolkien-and-c-s-lewis-legendary-friendship.html
Tollers was how Lewis referred to Tolkien.