Add email testing example (#4152)

* Add email testing example

Includes an example provided by  Jeremy

* Updated with suggestions

Co-authored-by: Jeremy Stretch <jeremy.stretch@networktocode.com>

docs/configuration/optional-settings.md

@@ -109,6 +109,14 @@ In order to send email, NetBox needs an email server configured. The following i
 * TIMEOUT - Amount of time to wait for a connection (seconds)
 * FROM_EMAIL - Sender address for emails sent by NetBox
 
+Email is sent from NetBox only for critical events. If you would like to test the email server configuration please use the django function [send_mail()]( https://docs.djangoproject.com/en/3.0/topics/email/#send-mail):
+
+```
+# python ./manage.py nbshell
+>>> from django.core.mail import send_mail
+>>> send_mail('Test Email Subject', 'Test Email Body', 'noreply-netbox@example.com', ['users@example.com'], fail_silently=False)
+```
+
 ---
 
 ## EXEMPT_VIEW_PERMISSIONS