More README notes

README.rst

@@ -25,7 +25,10 @@ works by storing email in the database for later sending. This has a number of
 advantages:
 
 - **robustness** - if your email provider goes down or has a temporary error,
-  the email won’t be lost.
+  the email won’t be lost. In addition, since the ``send_mail()`` call always
+  succeeds (unless your database is out of action), then the HTTP request that
+  triggered the email to be sent won’t crash, and any ongoing transaction won’t
+  be rolled back.
 
 - **correctness** - when an outgoing email is created as part of a transaction,
   since it is stored in the database it will participate in transactions. This
@@ -51,6 +54,10 @@ you'll either need to fall back to using Django's default mail backend, or
 increase your database limits (a procedure that depends on which database you
 are using).
 
+With django-mailer, you can’t know in a Django view function whether the email
+has actually been sent or not - the ``send_mail`` function just stores mail on
+the queue to be sent later.
+
 django-mailer was developed as part of the `Pinax ecosystem
 <http://pinaxproject.com>`_ but is just a Django app and can be used
 independently of other Pinax apps.