Suppress images for short emails

config/locales/server.en.yml

@@ -932,6 +932,9 @@ en:
 
     disable_emails: "Prevent Discourse from sending any kind of emails"
 
+    strip_images_from_short_emails: "Strip images from emails having size less than 2800 Bytes"
+    short_email_length: "Short email length in Bytes"
+
     pop3_polling_enabled: "Poll via POP3 for email replies."
     pop3_polling_ssl: "Use SSL while connecting to the POP3 server. (Recommended)"
     pop3_polling_period_mins: "The period in minutes between checking the POP3 account for email. NOTE: requires restart."

config/site_settings.yml

@@ -405,6 +405,8 @@ email:
   email_prefix: ''
   email_site_title: ''
   disable_emails: false
+  strip_images_from_short_emails: true
+  short_email_length: 2800
 
 files:
   max_image_size_kb:
@@ -783,4 +785,3 @@ uncategorized:
   privacy_topic_id:
     default: -1
     hidden: true
-

lib/email/sender.rb

@@ -94,6 +94,12 @@ module Email
       @message.header['X-Discourse-Post-Id'] = nil
       @message.header['X-Discourse-Reply-Key'] = nil
 
+      # Suppress images from short emails
+      if SiteSetting.strip_images_from_short_emails && @message.html_part.body.to_s.bytesize <= SiteSetting.short_email_length && @message.html_part.body =~ /<img[^>]+>/
+        style = Email::Styles.new(@message.html_part.body.to_s)
+        @message.html_part.body = style.strip_avatars_and_emojis
+      end
+
       begin
         @message.deliver
       rescue *SMTP_CLIENT_ERRORS => e

lib/email/styles.rb

@@ -137,6 +137,19 @@ module Email
       end
     end
 
+    def strip_avatars_and_emojis
+      @fragment.css('img').each do |img|
+        if img['src'] =~ /user_avatar/
+          img.remove
+        end
+
+        if img['src'] =~ /plugins\/emoji/
+          img.replace img['title']
+        end
+      end
+      return @fragment.to_s
+    end
+
     private
 
     def replace_relative_urls