Add images of inbound/outbound mail flows.

en_US/overview/0-used.components.md

@@ -97,10 +97,18 @@
 </tbody>
 </table>
 
-# The Big Picture
+## The Big Picture
 
 ![](./images/big.picture.png)
 
+## Mail Flow of Inbound Emails
+
+![](./images/flow.inbound.png)
+
+## Mail Flow of Outbound Emails
+
+![](./images/flow.outbound.png)
+
 # See also
 
 * [Locations of configuration and log files of major components](./file.locations.html)

html/used.components.html

@@ -106,8 +106,12 @@
 </tbody>
 </table>
 
-<h1 id="the-big-picture">The Big Picture</h1>
+<h2 id="the-big-picture">The Big Picture</h2>
 <p><img alt="" src="./images/big.picture.png" /></p>
+<h2 id="mail-flow-of-inbound-emails">Mail Flow of Inbound Emails</h2>
+<p><img alt="" src="./images/flow.inbound.png" /></p>
+<h2 id="mail-flow-of-outbound-emails">Mail Flow of Outbound Emails</h2>
+<p><img alt="" src="./images/flow.outbound.png" /></p>
 <h1 id="see-also">See also</h1>
 <ul>
 <li><a href="./file.locations.html">Locations of configuration and log files of major components</a></li>