FIX: don't use 'Return-Path' header to determine whether the email was auto generated

lib/email/receiver.rb

@@ -92,7 +92,6 @@ module Email
     end
 
     def is_auto_generated?
-      @mail.return_path.blank? ||
       @mail[:precedence].to_s[/list|junk|bulk|auto_reply/] ||
       @mail.header.to_s[/auto-(submitted|replied|generated)/]
     end

spec/components/email/receiver_spec.rb

@@ -29,10 +29,6 @@ describe Email::Receiver do
     expect { Email::Receiver.new(email(:missing_message_id)) }.to raise_error(Email::Receiver::NoMessageIdError)
   end
 
-  it "raises an AutoGeneratedEmailError when the mail has no return path" do
-    expect { process(:no_return_path) }.to raise_error(Email::Receiver::AutoGeneratedEmailError)
-  end
-
   it "raises an AutoGeneratedEmailError when the mail is auto generated" do
     expect { process(:auto_generated_precedence) }.to raise_error(Email::Receiver::AutoGeneratedEmailError)
     expect { process(:auto_generated_header) }.to raise_error(Email::Receiver::AutoGeneratedEmailError)