Gracefully handle SMTP user input errors (e.g. incorrect email addresses) to prevent Sidekiq retries

Closes https://github.com/gitlabhq/gitlabhq/issues/9560

CHANGELOG

@@ -6,6 +6,7 @@ v 8.0.0 (unreleased)
   - Faster merge
   - Ability to fetch merge requests from refs/merge-requests/:id
   - Allow displaying of archived projects in the admin interface (Artem Sidorenko)
+  - Gracefully handle SMTP user input errors (e.g. incorrect email addresses) to prevent Sidekiq retries (Stan Hu)
 
 v 7.14.0 (unreleased)
   - Update default robots.txt rules to disallow crawling of irrelevant pages (Ben Bodenmiller)

app/workers/emails_on_push_worker.rb

@@ -42,6 +42,7 @@ class EmailsOnPushWorker
     end
 
     recipients.split(" ").each do |recipient|
+      begin
         Notify.repository_push_email(
           project_id,
           recipient,
@@ -53,6 +54,10 @@ class EmailsOnPushWorker
           send_from_committer_email:  send_from_committer_email,
           disable_diffs:              disable_diffs
         ).deliver
+      # These are input errors and won't be corrected even if Sidekiq retries
+      rescue Net::SMTPFatalError, Net::SMTPSyntaxError => e
+        logger.info("Failed to send e-mail for project '#{project.name_with_namespace}' to #{recipient}: #{e}")
+      end
     end
   ensure
     compare = nil

spec/workers/emails_on_push_worker_spec.rb

@@ -0,0 +1,34 @@
+require 'spec_helper'
+
+describe EmailsOnPushWorker do
+  include RepoHelpers
+
+  let(:project) { create(:project) }
+  let(:user) { create(:user) }
+  let(:data) { Gitlab::PushDataBuilder.build_sample(project, user) }
+
+  subject { EmailsOnPushWorker.new }
+
+  before do
+    allow(Project).to receive(:find).and_return(project)
+  end
+
+  describe "#perform" do
+    it "sends mail" do
+      subject.perform(project.id, user.email, data.stringify_keys)
+
+      email = ActionMailer::Base.deliveries.last
+      expect(email.subject).to include('Change some files')
+      expect(email.to).to eq([user.email])
+    end
+
+    it "gracefully handles an input SMTP error" do
+      ActionMailer::Base.deliveries.clear
+      allow(Notify).to receive(:repository_push_email).and_raise(Net::SMTPFatalError)
+
+      subject.perform(project.id, user.email, data.stringify_keys)
+
+      expect(ActionMailer::Base.deliveries.count).to eq(0)
+    end
+  end
+end