diff --git a/lib/docurest/envelope.rb b/lib/docurest/envelope.rb
index 06ab72a..d74b6e1 100644
--- a/lib/docurest/envelope.rb
+++ b/lib/docurest/envelope.rb
@@ -94,10 +94,13 @@ module Docurest
         emailSubject: emailSubject,
         emailBlurb: emailBlurb,
         emailSettings: emailSettings.to_h,
-        documents: documents.map(&:to_h),
-        recipients: Docurest::Base.hash_by_type(recipients),
-        files: files,
-      }
+      }.tap do |hash|
+        if documents_changed?
+          hash[:documents] = documents.map(&:to_h)
+          hash[:files] = files
+        end
+        hash[:recipients] = Docurest::Base.hash_by_type(recipients) if recipients_changed?
+      end
     end
 
     private
diff --git a/lib/docurest/field.rb b/lib/docurest/field.rb
index 6e9423b..00307ec 100644
--- a/lib/docurest/field.rb
+++ b/lib/docurest/field.rb
@@ -45,8 +45,14 @@ module Docurest
 
         value.send("#{parent_field}=", guid) if parent_field
         value.id = values.length + 1 unless value.id
+
+        instance_variable_set(:"@#{klass}_changed", true)
+
         values << value
       end
+      define_method("#{klass}_changed?") do
+        !!instance_variable_get(:"@#{klass}_changed")
+      end
     end
   end
 end