doc (components): Add message cleaning section to email gateway doc:

fix 464

doc/components.rst

@@ -1009,6 +1009,28 @@ they are removed and added as blog tags (aka categories).
 Only the JID associated to the recipient of the mailing list can access the pubsub node.
 It will be possible to make a mailing list public in the future.
 
+.. _email-gateway-message-cleaning:
+
+Message Cleaning
+~~~~~~~~~~~~~~~~
+
+Emails often contain extraneous content that can make them harder to read. For example,
+replying to an email in a client typically includes the entire previous message as a
+quote. Similarly, mailing list software often appends signatures with
+subscription/unsubscription instructions.
+
+To improve readability, the email gateway automatically cleans up mailing list messages
+during conversion. First, all text-only messages are converted to XHTML for consistency.
+Then, it identifies and tags these “noisy” elements with a CSS class named ``noise``. This
+allows your XMPP client to selectively hide or visually distinguish these parts of the
+message.
+
+The original content is preserved; the ``noise`` class simply provides a way for your
+client to present the message more clearly. This means you can still view the full
+original message if desired. The gateway attempts to intelligently detect noisy elements,
+but it’s possible for some content to be incorrectly identified.
+
+
 
 .. _XEP-0033 (Extended Stanza Addressing): https://xmpp.org/extensions/xep-0033.html
 .. _XEP-0100 (Gateway Interaction): https://xmpp.org/extensions/xep-0100.html