SMTP: Add documentation for notification service call (#18038)

source/_integrations/smtp.markdown

@@ -36,7 +36,7 @@ sender:
   required: true
   type: string
 recipient:
-  description: E-mail address of the recipient of the notification. This can be a recipient address or a list of addresses for multiple recipients.
+  description: Default E-mail address of the recipient of the notification. This can be a recipient address or a list of addresses for multiple recipients.<br>This is where you want to send your E-mail notifications by default (when not specifying `target` in the service call). Any E-mail address(es) specified in the service call's `target` field will override this recipient content.
   required: true
   type: [list, string]
 server:
@@ -85,16 +85,16 @@ A sample configuration entry for Google Mail.
 notify:
   - name: "NOTIFIER_NAME"
     platform: smtp
-    server: "smtp.gmail.com"
+    server: "smtp.example.com"
     port: 587
     timeout: 15
-    sender: "john@gmail.com"
+    sender: "john@example.com"
     encryption: starttls
-    username: "john@gmail.com"
+    username: "john@example.com"
     password: "thePassword"
     recipient:
-      - "james@gmail.com"
-      - "bob@gmail.com"
+      - "james@example.com"
+      - "bob@example.com"
     sender_name: "My Home Assistant"
 ```
 
@@ -113,12 +113,16 @@ burglar:
       data:
           title: "Intruder alert"
           message: "Intruder alert at apartment!!"
+          target:
+            - "my_intruder_alert@example.com"
           data:
               images:
                   - /home/pi/snapshot1.jpg
                   - /home/pi/snapshot2.jpg
 ```
 
+The optional `target` field is used to specify recipient(s) for this specific service call. When `target` field is not used, this message will be sent to default recipient(s), in this example, james@example.com and bob@example.com.
+
 The optional `images` field adds in-line image attachments to the email. This sends a text/HTML multi-part message instead of the plain text default.
 
 The optional `html` field makes a custom text/HTML multi-part message, allowing total freedom for sending rich html emails. In them, if you need to attach images, you can pass both arguments (`html` and `images`), the attachments will be joined with the basename of the images, so they can be included in the html page with `src="cid:image_name.ext"`.