Email Not working

OS: Linux CustomerSuccessBox 4.4.0-21-generic #37-Ubuntu SMP Mon Apr 18 18:33:37 UTC 2016 x86_64
PHP: Linux 5.6.30-10+deb.sury.org~xenial+2 en_US.UTF-8
PHP Dependencies: iconv=Yes, spl_autoload=Yes, openssl=Yes, sockets=Yes, allow_url_fopen=Yes, mcrypt=No, zlib_encode=Yes
WordPress: 4.7.7 en_US UTF-8
WordPress Theme: Total
WordPress Plugins: Gravity Forms, Ultimate Addons for Visual Composer, All-in-One Custom Backgrounds Lite, iThemes Security, Contact Form 7, Duplicate Post, Favicon by RealFaviconGenerator, File Manager, Anti-Malware Security and Brute-Force Firewall, Gravity Forms Zoho CRM Add-On, HubSpot Tracking Code for WordPress, WPBakery Visual Composer, HubSpot Marketing Free (formerly Leadin), P3 (Plugin Performance Profiler), Post SMTP, SparkPost, Theme Authenticity Checker (TAC), Vafpress Framework Plugin, W3 Total Cache, Wordfence Security, Yoast SEO
WordPress wp_mail Filter(s): wp_staticize_emoji_for_email
WordPress wp_mail_from Filter(s): wordfence::fixWPMailFromAddress
WordPress phpmailer_init Action(s): wpcf7_phpmailer_init
Postman: 1.7.10
Postman Sender Domain (Envelope|Message): customersuccessbox.com | customersuccessbox.com
Postman Prevent Message Sender Override (Email|Name): No | No
Postman Active Transport: SMTP (smtps:plain://smtp.gmail.com:587)
Postman Active Transport Status (Ready|Connected): Yes | Yes
Postman Deliveries (Success|Fail): 521 | 180