
The bottom line is that the law is on your side. Print and keep the email to create a paper trail, and CC the neighborhood with the rest of your notes, which should include copies of the state statutes about your rights to keep chickens, so you're protected. Interestingly, when people see a CC list, they tend to check themselves and stop bullying.
Suggest he plant shrubs and build a privacy fence...
And, honestly it's tough for me to say this, because I get fired up over stupidity like this too... write your emails, but don't send them until you have slept and have a chance to read them again for perspective and judgement. It'll help everyone stay on the high road.