Only use HTML templates for the digest email.

app/controllers/admin/email_controller.rb

@@ -30,7 +30,7 @@ class Admin::EmailController < Admin::AdminController
 
   def preview_digest
     params.require(:last_seen_at)
-    renderer = EmailRenderer.new(UserNotifications.digest(current_user, since: params[:last_seen_at]))
+    renderer = EmailRenderer.new(UserNotifications.digest(current_user, since: params[:last_seen_at]), html_template: true)
     render json: MultiJson.dump(html_content: renderer.html, text_content: renderer.text)
   end
 

app/views/email/template.html.erb

@@ -1,4 +1,4 @@
-<table style="border: 1px solid #ddd;">
+<table style="border: 1px solid #ddd;" cellspacing="0" cellpadding="0">
 <tr>
   <td style="padding: 10px 10px; background-color: #eee; border: 1px solid #ddd;">
     <a href="<%= Discourse.base_url %>">
@@ -6,7 +6,7 @@
   </td>
 </tr>
 <tr>
-  <td style="background-color: #fff; padding: 0 10px; font-family: Arial, Helvetica, sans-serif; font-size: 14px;">
+  <td style="background-color: #fff; padding: 10px 10px; font-family: Arial, Helvetica, sans-serif; font-size: 14px;">
     <%= raw(html_body) %>
   </td>
 </tr>

lib/email_renderer.rb

@@ -2,28 +2,35 @@ require_dependency 'email_styles'
 
 class EmailRenderer
 
-  def initialize(message)
+  def initialize(message, opts=nil)
     @message = message
+    @opts = opts || {}
   end
 
   def text
     @text ||= @message.body.to_s.force_encoding('UTF-8')
   end
 
-  def html
+  def logo_url
-    formatted_body = EmailStyles.new(PrettyText.cook(text, environment: 'email')).format
-
     logo_url = SiteSetting.logo_url
     if logo_url !~ /http(s)?\:\/\//
       logo_url = "#{Discourse.base_url}#{logo_url}"
     end
+    logo_url
+  end
 
+  def html
+    formatted_body = EmailStyles.new(PrettyText.cook(text, environment: 'email')).format
+
+    if @opts[:html_template]
       ActionView::Base.new(Rails.configuration.paths["app/views"]).render(
         template: 'email/template',
         format: :html,
-      locals: { html_body: formatted_body,
+        locals: { html_body: formatted_body, logo_url: logo_url }
-                logo_url: logo_url }
       )
+    else
+      formatted_body
+    end
   end
 
 end

lib/email_sender.rb

@@ -22,7 +22,14 @@ class EmailSender
     return if @message.body.blank?
 
     @message.charset = 'UTF-8'
-    renderer = EmailRenderer.new(@message)
+
+    opts = {}
+
+    # Only use the html template on digest emails
+    opts[:html_template] = true if (@email_type == 'digest')
+
+    renderer = EmailRenderer.new(@message, opts)
+
     @message.html_part = Mail::Part.new do
       content_type 'text/html; charset=UTF-8'
       body renderer.html