docs: add note about protocols to getting started

docs/tutorials/getting_started.rst

@@ -40,6 +40,11 @@ There are guides to set up the following email providers:
 - :ref:`config-gmail`
 - :ref:`config-outlook`
 
+.. note::
+
+    By default, Red Mail uses **STARTTLS** as the protocol.
+    This is suitable for majority of cases but if you need
+    to use **SSL**, **TLS** or other protocols, see :ref:`config-smtp`.
 
 Sending Emails
 --------------