FEATURE: new disable_emails site setting

config/locales/server.en.yml

@@ -921,6 +921,8 @@ en:
     reply_by_email_enabled: "Enable replying to topics via email."
     reply_by_email_address: "Template for reply by email incoming email address, for example: %{reply_key}@reply.example.com or replies+%{reply_key}@example.com"
 
+    disable_emails: "Prevent Discourse from sending any kind of emails"
+
     pop3s_polling_enabled: "Poll via POP3S for email replies."
     pop3s_polling_insecure: "Poll using plain text POP3 without SSL."
     pop3s_polling_period_mins: "The period in minutes between checking the POP3S account for email. NOTE: requires restart."

config/site_settings.yml

@@ -395,6 +395,7 @@ email:
     enum: 'TrustLevelSetting'
   email_prefix: ''
   email_site_title: ''
+  disable_emails: false
 
 files:
   max_image_size_kb:

lib/email/sender.rb

@@ -22,6 +22,7 @@ module Email
     end
 
     def send
+      return if SiteSetting.disable_emails
       return skip(I18n.t('email_log.message_blank')) if @message.blank?
       return skip(I18n.t('email_log.message_to_blank')) if @message.to.blank?
 

spec/components/email/sender_spec.rb

@@ -3,6 +3,13 @@ require 'email/sender'
 
 describe Email::Sender do
 
+  it "doesn't deliver mail when mails are disabled" do
+    SiteSetting.expects(:disable_emails).returns(true)
+    Mail::Message.any_instance.expects(:deliver).never
+    message = Mail::Message.new(to: "hello@world.com" , body: "hello")
+    Email::Sender.new(message, :hello).send
+  end
+
   it "doesn't deliver mail when the message is nil" do
     Mail::Message.any_instance.expects(:deliver).never
     Email::Sender.new(nil, :hello).send