Bug in Mail::Address

_test.rb

#!/usr/bin/env ruby
# encoding: utf-8

require 'bundler/setup'
require 'mail'

def formatted_email(name, email)
  address = Mail::Address.new(email)
  address.display_name = name
  address.format
end

def test name, email
  puts 'BEFORE'
  puts '======'
  puts "name: #{name} (#{name.encoding})"
  puts "email: #{email} (#{email.encoding})"
  puts "\n"

  formatted = formatted_email(name, email)

  puts 'AFTER'
  puts '====='
  puts "formatted: #{formatted} (#{formatted.encoding})"
  puts "name: #{name} (#{name.encoding})"
  puts "email: #{email} (#{email.encoding})"
  puts "\n"
end

test 'Joe', 'joe@example.com'
test 'Zoé', 'zoe@example.com'

output-mail-2.5.3.txt

BEFORE
======
name: Joe (UTF-8)
email: joe@example.com (UTF-8)

AFTER
=====
formatted: Joe <joe@example.com> (UTF-8)
name: Joe (UTF-8)
email: joe@example.com (UTF-8)

BEFORE
======
name: Zoé (UTF-8)
email: zoe@example.com (UTF-8)

AFTER
=====
formatted: =?UTF-8?B?Wm/DqQ==?= <zoe@example.com> (UTF-8)
name: Zoé (UTF-8)
email: zoe@example.com (UTF-8)

output-mail-2.5.4.txt

BEFORE
======
name: Joe (UTF-8)
email: joe@example.com (UTF-8)

AFTER
=====
formatted: Joe <joe@example.com> (UTF-8)
name: Joe (UTF-8)
email: joe@example.com (UTF-8)

BEFORE
======
name: Zoé (UTF-8)
email: zoe@example.com (UTF-8)

AFTER
=====
formatted: "Zoé" <zoe@example.com> (UTF-8)
name: Zoé (ASCII-8BIT)
email: zoe@example.com (UTF-8)