DEV: Add created_via column to IncomingEmail (#11751)

This should make it easier to track down how the incoming email was created, which is one of four locations:

The POP3 poller (which picks up reply via email replies)
The admin email controller #handle_mail (which is where hosted mail is sent)
The IMAP sync tool
The group SMTP mailer, which sends emails when replying to IMAP topics, pre-emptively creating IncomingEmail records to avoid double syncing

spec/components/email/receiver_spec.rb

@@ -11,8 +11,8 @@ describe Email::Receiver do
     SiteSetting.alternative_reply_by_email_addresses = "alt+%{reply_key}@bar.com"
   end
 
-  def process(email_name)
-    Email::Receiver.new(email(email_name)).process!
+  def process(email_name, opts = {})
+    Email::Receiver.new(email(email_name), opts).process!
   end
 
   it "raises an EmptyEmailError when 'mail_string' is blank" do
@@ -350,6 +350,13 @@ describe Email::Receiver do
       expect(topic.posts.last.raw).to eq("This is a **HTML** reply ;)")
     end
 
+    it "stores the created_via source against the incoming email" do
+      process(:text_reply, source: :handle_mail)
+      expect(IncomingEmail.last.created_via).to eq(IncomingEmail.created_via_types[:handle_mail])
+      process(:text_and_html_reply, source: :imap)
+      expect(IncomingEmail.last.created_via).to eq(IncomingEmail.created_via_types[:imap])
+    end
+
     it "automatically elides gmail quotes" do
       SiteSetting.always_show_trimmed_content = true
       expect { process(:gmail_html_reply) }.to change { topic.posts.count }