Ignore empty incoming messages.

app/mailers/email_rejection_mailer.rb

@@ -3,6 +3,8 @@ class EmailRejectionMailer < BaseMailer
     @reason = reason
     @original_message = Mail::Message.new(original_raw)
+    return unless @original_message.from
+
     headers = {
       to: @original_message.from,
       subject: "[Rejected] #{@original_message.subject}"

app/workers/email_receiver_worker.rb

@@ -18,6 +18,8 @@ class EmailReceiverWorker
   def handle_failure(raw, e)
     Rails.logger.warn("Email can not be processed: #{e}\n\n#{raw}")
+    return unless raw.present?
+
     can_retry = false
     reason = nil

config/mail_room.yml.example

@@ -14,6 +14,8 @@
     # :name: "inbox"
     # # Always "sidekiq".
     # :delivery_method: sidekiq
+    # # Always true.
+    # :delete_after_delivery: true
     # :delivery_options:
     #   # The URL to the Redis server used by Sidekiq. Should match the URL in config/resque.yml.
     #   :redis_url: redis://localhost:6379

doc/reply_by_email/README.md

@@ -59,6 +59,8 @@ In this example, we'll use the Gmail address `gitlab-replies@gmail.com`. If you'
         :name: "inbox"
         # Always "sidekiq".
         :delivery_method: sidekiq
+        # Always true.
+        :delete_after_delivery: true
         :delivery_options:
           # The URL to the Redis server used by Sidekiq. Should match the URL in config/resque.yml.
           :redis_url: redis://localhost:6379
@@ -144,6 +146,8 @@ TODO
         :name: "inbox"
         # Always "sidekiq".
         :delivery_method: sidekiq
+        # Always true.
+        :delete_after_delivery: true
         :delivery_options:
           # The URL to the Redis server used by Sidekiq. Should match the URL in config/resque.yml.
           :redis_url: redis://localhost:6379