FIX: Again, try to get a flexible absolute logo_url

app/helpers/application_helper.rb

@@ -12,7 +12,7 @@ module ApplicationHelper
 
   def discourse_csrf_tags
     # anon can not have a CSRF token cause these are all pages
-    # that may be cached, causing a mismatch between session CSRF 
+    # that may be cached, causing a mismatch between session CSRF
     # and CSRF on page and horrible impossible to debug login issues
     if current_user
       csrf_meta_tags

app/views/email/template.html.erb

@@ -7,7 +7,7 @@
   <tr>
     <td>
       <a href="<%= Discourse.base_url %>">
-      <%= image_tag(SiteSetting.logo_url, style: "height: 50px; margin-bottom: 15px; ") %>
+      <img src="<%= logo_url %>" style="height: 50px; margin-bottom: 15px;"></a>
     </td>
   </tr>
   <tr>

lib/email_renderer.rb

@@ -13,10 +13,16 @@ class EmailRenderer
   def html
     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
+
     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 }
     )
   end