Check out The Perils of 'Contact Me' by Ben Yagoda, most recently the author of Memoir: A History, on the fun and irritation of receiving emails in response to one's writing.
I've never received a cranky or irritating email in response to my writing, though one of the chapters from my book did offend the political sensibilities of a literary journal editor to the point that he wrote me a two-page rejection email.
The most gratifying emails I receive are those in which the writer says that they were so glad to see someone writing about religion and its intersection with culture in a way that isn't dismissive.
But the emails closest to my heart are those from male college students (who have probably been forced to read my book for some class) who say something like, "at first I hated it, then I got to the chapter about Pulp Fiction and it got good." I see my college-aged self in those emails.
One of the best coorespondences between writer and reader I've ever read took place between Flannery O'Connor and a woman who had picked up her work on a whim.
The woman wrote to say that when she came home at the end of the day she wanted to read something that would uplift her and O'Connor's work had not.
O'Connor wrote back to say that if her heart had been in the right place she would have been uplifted. Burn.