diff --git a/mailer.rst b/mailer.rst
index 3b83c5454ec..a2c7d6a5b6a 100644
--- a/mailer.rst
+++ b/mailer.rst
@@ -623,6 +623,19 @@ environment:
 
     If you're using Messenger and routing to a transport, the message will *still*
     be sent to that transport.
+    
+Save Messages in Files
+~~~~~~~~~~~~~~~~~~~~~~
+
+While developing (or testing), you may want to save messages in the filesystem.
+You can do this by forcing Mailer to use the ``FileTransport`` like this:
+
+.. code-block:: yaml
+
+    # config/packages/test/mailer.yaml
+    framework:
+        mailer:
+            dsn: 'file://%kernel.project_dir%/var/emails'
 
 Always Send to the Same Address
 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~