diff --git a/config/initializers/mail_extensions.rb b/config/initializers/mail_extensions.rb
index a64974d..c109fa7 100644
--- a/config/initializers/mail_extensions.rb
+++ b/config/initializers/mail_extensions.rb
@@ -115,10 +115,10 @@ module Mail
     def initialize(parts_list)
       @parts_list = parts_list
       @content_disposition_type = "attachment"
-      parts_list.map do |p|
+      parts = parts_list.map do |p|
         p.parts.empty? && p.attachment? ? p : p.attachments
-      end.flatten.compact.each { |a| self << a }
-      self
+      end.flatten.compact
+      parts.each { |a| self << a }
     end
     # rubocop:enable Lint/MissingSuper
 
diff --git a/lib/postal/dkim_header.rb b/lib/postal/dkim_header.rb
index 3721e32..36f7094 100644
--- a/lib/postal/dkim_header.rb
+++ b/lib/postal/dkim_header.rb
@@ -34,14 +34,15 @@ module Postal
 
     def normalized_headers
       [].tap do |new_headers|
-        headers.select { |h|
+        dkim_headers = headers.select { |h|
           h.match(%r{
             ^(
               from|sender|reply-to|subject|date|message-id|to|cc|mime-version|content-type|content-transfer-encoding|
               resent-to|resent-cc|resent-from|resent-sender|resent-message-id|in-reply-to|references|list-id|list-help|
               list-owner|list-unsubscribe|list-subscribe|list-post
             ):}ix)
-        }.each do |h|
+        }
+        dkim_headers.each do |h|
           new_headers << normalize_header(h)
         end
       end