Edited version: What are great examples of comprehensively archived mathematical correspondence (including both handwritten and electronic items)?
Previous version :
How should mathematicians archive their work-related output?
Context: here I'm thinking about drafts, and correspondence between mathematicians, either in the form of handwritten material or of emails. For example, I would find it fascinating to read, say, the collection of Letters that Deligne sent to lots of people over the years (and the replies) , or the email exchanges between Green and Tao culminating in their theorem on primes in arithmetic progression.
 Some have been archived at IAS https://publications.ias.edu/book/export/html/2582 but they are missing lots of others like a letter to Cvitanovic https://birdtracks.eu/extras/Deligne96.pdf or those to Bar-Natan https://www.math.toronto.edu/~drorbn/Deligne/