minor #16589 [Mailer] Update mailer.rst (mark2016)

This PR was submitted for the 6.0 branch but it was squashed and merged into the 5.4 branch instead.

Discussion
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[Mailer] Update mailer.rst

Added a Tip to clarify that no async emails will be sent unless consumed by a worker.

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Commits
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7db951d [Mailer] Update mailer.rst

Author: javiereguiluz

mailer.rst

@@ -368,6 +368,17 @@ and create an :class:`Symfony\\Component\\Mime\\Email` object::
 
 That's it! The message will be sent via the transport you configured.
 
+.. tip::
+    
+    If the transport is configured to send emails asynchronously, then no email will
+    be sent until a worker consumes it.  To send queued emails, run console commands as
+    specified in :doc:`Consuming Messages (Running the Worker) <messenger-worker>`.
+    Also ensure the PHP timezone in php.ini is set correctly for your region for both
+    the CLI php.ini and webserver php.ini, this ensures the timestamp that the worker
+    sees aligns to the timestamp recorded on the email in the message queue. (Sometimes
+    the CLI and webserver will read different php.ini files, depending on environment 
+    setup).
+
 Email Addresses
 ~~~~~~~~~~~~~~~