postfix: add page (#3875)

pages/linux/postfix.md

@@ -0,0 +1,29 @@
+# postfix
+
+> Postfix mail transfer agent (MTA) control program.
+> See also `dovecot`, a mail delivery agent (MDA) that integrates with Postfix.
+> More information: <http://postfix.org>.
+
+- Check the configuration:
+
+`sudo postfix check`
+
+- Check the status of the Postfix daemon:
+
+`sudo postfix status`
+
+- Start Postfix:
+
+`sudo postfix start`
+
+- Gracefully stop Postfix:
+
+`sudo postfix stop`
+
+- Flush the mail queue:
+
+`sudo postfix flush`
+
+- Reload the configuration files:
+
+`sudo postfix reload`