Minor tweaks

Author: javiereguiluz

components/mailer.rst

@@ -102,13 +102,17 @@ binary. For third-party providers, refers to the following table:
 Failover Transport
 ------------------
 
-You can create failover transport with the help of `failover()` keyword::
+You can create failover transport with the help of ``failover()`` keyword::
 
     $dsn = 'failover(api://id@postmark smtp://key@sendgrid)';
 
 So if the first transport fails, the mailer will attempt to send through the
 second transport.
 
+.. versionadded:: 4.4
+
+    The ``failover()`` keyword was introduced in Symfony 4.4.
+
 Round Robin
 -----------
 
@@ -117,6 +121,10 @@ you can use the ``roundrobin()`` keyword with the transports::
 
     $dsn = 'roundrobin(api://id@postmark smtp://key@sendgrid)'
 
+.. versionadded:: 4.4
+
+    The ``roundrobin()`` keyword was introduced in Symfony 4.4.
+
 Sending emails asynchronously
 -----------------------------