I should also mention any controversies or discussions around this. For instance, the authenticity of the letters in digital versions—ensuring they are genuine or historically accurate. Or the impact on privacy if old letters are being republished without permission.
Yes. Check "Kaththu Kaththu Kannuneer" by K. K. (Kerala Bhasha Institute) and "Pracheena Malayala Premalekhanakal" (out of print, but available as scanned PDF on archive.org). Malayalam Premalekhanam Pdf