Encode domain parts of all addresses in mailers as punycode

app/mailers/interceptors/punycode_interceptor.rb

@@ -0,0 +1,24 @@
+class PunycodeInterceptor
+  class << self
+    def delivering_email(message)
+      message.from = encode_addresses_as_punycode(message.from)
+      message.to = encode_addresses_as_punycode(message.to)
+      message.cc = encode_addresses_as_punycode(message.cc) if message.cc
+      message.bcc = encode_addresses_as_punycode(message.bcc) if message.bcc
+    end
+
+    private
+
+    def encode_addresses_as_punycode(addresses)
+      addresses.map do |address|
+        local_part, domain_part = address.split('@')
+        domain_part = encode_domain_part_as_punycode(domain_part)
+        [local_part, '@', domain_part].join
+      end
+    end
+
+    def encode_domain_part_as_punycode(domain_part)
+      SimpleIDN.to_ascii(domain_part)
+    end
+  end
+end