Looking For A Dataset Of Letters. Any Ideas?

I’m doing a project for a website where I analyze the similarity in writing style and content of letters of different users and try to match them to another user with the highest similarity. I need a dataset of letters/emails/long text messages for that and that’s what I’m looking for. I’ve found the subreddits r/letters and r/loveletters but they haven’t been too satisfactory in terms of the quality of texts. I’ve thought about making dataset with sample letter texts from English exams but since there is no one authentic human writer behind it, it’s not the best source either. Historic archives exist but since my focus is on modern casual letter/email writing, I’ve decided to pass on that. If there was a blog, for example, where someone publicly wrote letters to someone, that would be great but I am unable to find any. Any help would be must appreciated!