better email deliverability guidance

config/locales/server.en.yml

@@ -648,7 +648,7 @@ en:
     mobile_logo_url: "The logo used for mobile browsers. If left blank, `logo_url` will be used. eg: http://example.com/uploads/default/logo.png"
     apple_touch_icon_url: "Icon used for Apple touch devices. Recommended size is 144px by 144px."
 
-    notification_email: "The return email address used when sending system emails such as notifying users of lost passwords, new accounts etc"
+    notification_email: "The from: email address used when sending all essential system emails. The domain specified here must have SPF, DKIM and reverse PTR records set correctly for email to arrive."
     email_custom_headers: "A pipe-delimited list of custom email headers"
     use_https: "Should the full url for the site (Discourse.base_url) be http or https? DO NOT ENABLE THIS UNLESS HTTPS IS ALREADY SET UP AND WORKING!"
     summary_score_threshold: "The minimum score of a post to be included in the 'summary'"
@@ -1086,6 +1086,8 @@ en:
 
       Email deliverability is complicated. Here are a few important things you should check first:
 
+      - The domain in the "from" address of the email you send is what will be validated against. Be *sure* to set this correctly in your site settings as `notification email`.
+
       - Know how to view the *raw source of the email* in your mail client, so you can examine the email headers for important clues. in Gmail, it is the "show original" option in the drop-down menu on each mail.
 
       - **IMPORTANT:** Does your ISP have a reverse DNS record entered to associate the domain names and IP addresses you send mail from? [Test your Reverse PTR record][2] here. If your ISP does not enter the proper reverse DNS pointer record, it's very unlikely any of your email will be delivered.
@@ -1096,7 +1098,7 @@ en:
 
       - Verify that your email server is *definitely* sending a fully-qualified hostname that resolves in DNS in its HELO message. If not, this will cause your email to be rejected by many mail services.
 
-      - Configure [DKIM email key signing][3] in your email software, and place the public DKIM key in your DNS records. This is not required, but will significantly improve email deliverability.
+      - Configure [DKIM email key signing][3], and place the public DKIM key in your domain's DNS records. This is not required, but will significantly improve email deliverability. [Test your DKIM record][7] here.
 
       (The *easy* way is to [sign up for Mandrill][6], which has a generous free mailing plan and will be fine for small forums. You'll still need to set up the SPF and DKIM records in your DNS, though!)
 
@@ -1113,6 +1115,7 @@ en:
       [4]: http://whatismyipaddress.com/blacklist-check
       [5]: %{base_url}/unsubscribe
       [6]: http://mandrill.com
+      [7]: http://dkimcore.org/tools/dkimrecordcheck.html
 
       ----