lets do this

staging_mail_disable.php

@@ -0,0 +1,27 @@
+<?php
+/*
+Plugin Name: Staging Mail Disable
+Plugin URI: https://cooini.com/services/dev/wordpress
+Description: This plugin will disable will add a filter that prevents wordpress from sending mail
+Version: 1.0
+Author: sbyrd
+Author URI: https://cooini.com/
+License: MINE-all-mine
+*/
+
+
+$constant_requirements = ['WP_ENVIRONMENT_TYPE'=>'staging'];
+$plugins = ['fluent-smtp/fluent-smtp.php'];
+
+//Loop through our constants requirements
+foreach($constant_requirements as $constant => $requirement)
+{
+    if (constant($constant) === $requirement)
+    {
+        add_filter('pre_wp_mail', 'staging_mail_disabler');
+    }
+}
+
+function staging_mail_disabler() {
+    return false;
+}

wp-staging-plugin-disabler.php

@@ -25,4 +25,3 @@ foreach($constant_requirements as $constant => $requirement)
         break; // We only need one constant requirement to be meet
     }
 }
-