Test and seed email subject line

_docs/_developer_guide/platform_wide/sending_test_messages.md

@@ -56,6 +56,10 @@ If you're only testing email messages, you do not necessarily have to set up a t
 
 ![A Braze campaign with the Test Send tab selected][5]
 
+{% alert tip %} 
+You can also enable or disable [TEST (or SEED)][14] being appended on your test messages.
+{% endalert %}
+
 
 ## Testing from the command line
 
@@ -199,3 +203,4 @@ There are a few situations where test messages don't have complete feature parit
 [13]: {{site.baseurl}}/api/endpoints/messaging/
 [66]: {{site.baseurl}}/api/endpoints/messaging/send_messages/post_send_messages/
 [16]: {{site.baseurl}}/user_guide/message_building_by_channel/email/managing_user_subscriptions/#subscription-groups
+[14]: {{site.baseurl}}/user_guide/administrative/app_settings/manage_app_group/email_settings/#test-and-seed-subject-lines

_docs/_user_guide/administrative/app_settings/manage_app_group/email_settings.md

@@ -111,11 +111,11 @@ Once saved, Braze will send special instructions to the ESP in order to place th
 SSL enablement will wrap the URL of the tracking pixel with HTTPS instead of HTTP - if your SSL is misconfigured, it may affect the efficacy of the tracking pixel. 
 {% endalert %}
 
-## Toggle-Capable Features
+## Toggle features
 
 ![][2]{: style="float:right;max-width:30%;margin-left:15px;"}
 
-The three email settings listed are features that require no additional action other than toggling it on or off by using the corresponding switch. Read each setting for further details.
+The four email settings listed are features that require no additional action other than toggling it on or off by using the corresponding switch. Read each setting for further details.
 
 ### Resubscribe users when their email changes
 
@@ -158,6 +158,12 @@ CSS inlining is a technique that automatically inlines CSS styles for your email
 Changing this setting will not affect any of your existing email messages or templates. You can override this default at any time while composing messages or templates.
 
 For more information, refer to [CSS inlining][10].
+
+### Test and seed subject lines
+
+When toggled on, this will append the word "[TEST]" for emails sent as a test, or "[SEED]" when emails are send to your users. By default, this feature is disabled.
+
+![Test and Seed Email Subject Lines section in the Email Settings page.][14]
 
 [00]: {% image_buster /assets/img_archive/list_unsub_img1.png %}
 [0]: {% image_buster /assets/img/email_settings/custom_footer.png %}
@@ -173,4 +179,5 @@ For more information, refer to [CSS inlining][10].
 [11]: {% image_buster /assets/img/email_settings/bcc_address.png %}
 [12]: {% image_buster /assets/img/email_settings/require_bcc.png %}
 [13]: {% image_buster /assets/img/open_pixel.png %}
+[14]: {% image_buster /assets/img_archive/test_and_seed_email_subject_line.png %}
 [59]: {% image_buster /assets/img_archive/list_unsub_img3_new.png %}