Create envelope to validate mail

lib/gravity_mailbox/rails_cache_delivery_method.rb

@@ -14,6 +14,10 @@ def initialize(settings)
     end
 
     def deliver!(mail)
+      # https://github.com/mikel/mail/blob/d1d65b370b109b98e673a934e8b70a0c1f58cc59/lib/mail/network/delivery_methods/test_mailer.rb#L39
+      # Create the envelope to validate it
+      Mail::SmtpEnvelope.new(mail)
+
       key = "#{KEY_PREFIX}#{mail.message_id}"
       Rails.cache.write(key, mail.encoded, expires_in: 1.week) # TODO: setting for expiration
       actual_list = self.class.mail_keys

spec/gravity_mailbox/rails_cache_delivery_method_spec.rb

@@ -7,6 +7,8 @@
     let(:mail) do
       Mail.new.tap do |m|
         m.message_id = '123'
+        m.from = 'sender@example.com'
+        m.to = 'recipient@example.com'
       end
     end
 
@@ -26,6 +28,48 @@
         ["gravity_mailbox/#{mail.message_id}"]
       )
     end
+
+    describe 'envelope validation' do
+      context 'when mail has no sender' do
+        let(:mail) do
+          Mail.new.tap do |m|
+            m.message_id = '123'
+            m.to = 'recipient@example.com'
+          end
+        end
+
+        it 'raises an error' do
+          expect { delivering }.to raise_error(ArgumentError, /SMTP From address may not be blank/)
+        end
+      end
+
+      context 'when mail has no recipients' do
+        let(:mail) do
+          Mail.new.tap do |m|
+            m.message_id = '123'
+            m.from = 'sender@example.com'
+          end
+        end
+
+        it 'raises an error' do
+          expect { delivering }.to raise_error(ArgumentError, /SMTP To address may not be blank/)
+        end
+      end
+
+      context 'when mail has invalid from address' do
+        let(:mail) do
+          Mail.new.tap do |m|
+            m.message_id = '123'
+            m.from = ''
+            m.to = 'recipient@example.com'
+          end
+        end
+
+        it 'raises an error' do
+          expect { delivering }.to raise_error(ArgumentError, /SMTP From address may not be blank/)
+        end
+      end
+    end
   end
 
   describe '#mails' do