While everyone is here suggesting other epistolary novels to have emailed, I'd like to suggest Winter Letters by Agustin Fernández Paz. It would be much shorter than Dracula (i think it's just a few weeks maybe?) but it's really good and creepy and not enough ppl know about it imo
Edit: I just realized that since the book isn't out of copyright it wouldn't be possible but I still highly recommend reading it!!