tell application "Address Book"
	-- Go through each record.
	repeat with thePerson in every person
		
		-- A person can have multiple e-mail addresses.
		repeat with account in email of thePerson
			set emailAddress to value of account
			
			-- Use Python to get the lowercase version This is less verbose than doing it all in AppleScript.
			-- Set up to avoid a "privilege violation" error.
			tell current application
				set formatted to do shell script "python -c \"print '" & emailAddress & "'.lower()\""
			end tell
			
			set value of account to formatted
		end repeat
	end repeat
	
	-- Save all Address Book changes.
	save
end tell