feat: Support Azure single-tenant application using the Graph API (#6728) (#6878)

lib/microsoft_graph_delivery_method.rb

@@ -0,0 +1,26 @@
+# Recently (around Feb/Mar 2023), Microsoft has made sending
+# email through SMTP with Outlook near impossible, at least
+# for single tenant applications.
+#
+# As such, adding a delivery method to use the Microsoft Graph
+# API allows for emails to be sent again.
+require 'base64'
+
+class MicrosoftGraphDeliveryMethod
+  def initialize(config)
+    @config = config
+  end
+
+  def deliver!(mail)
+    # Create a new API connection, and post the mail to the `me/sendMail` endpoint.
+    # https://learn.microsoft.com/en-us/graph/api/user-sendmail#example-4-send-a-new-message-using-mime-format
+
+    headers = {
+      'Content-Type' => 'text/plain'
+    }
+    body = Base64.encode64(mail.to_s)
+
+    graph = MicrosoftGraphApi.new(@config[:token])
+    graph.post_to_api('me/sendMail', headers, body)
+  end
+end