I have some collections of letters on my shelves, a few by famous writers from different continents. These letters gave me an insight into the writing process of these writers. Sometimes there were letters about pencils and paperblocks. Other letters tell of the people they have met and have influenced the, Or contact with the publishing house. I have a collection of letters (not the original ones, mind you, but in a printed book) by Isak Dinesen, who wrote about her coffee plantation at Ngong, near Nairobi.
One of the most important writers from Southern Africa is Bessie Head (1937-1986), she did some writing, not just books but also letters. Read more about these letters here.