I am able to send a test email successfully.
Here is the diagnostic report:
Mailer: postsmtp
HostName: sccenter.org
cURL Version: 8.5.0
OpenSSL Version: OpenSSL/1.1.1w
OS: Linux jag02.verustech.com 3.10.0-327.36.3.el7.centos.plus.x86_64 #1 SMP Tue Oct 25 03:09:35 UTC 2016 x86_64
PHP: Linux 7.4.33 C
PHP Dependencies: iconv=Yes, spl_autoload=Yes, openssl=Yes, sockets=No, allow_url_fopen=No, mcrypt=No, zlib_encode=Yes
WordPress: 6.4.2 en_US UTF-8
WordPress Theme: Panoramic Child
WordPress Plugins: FooGallery, Accordions Combo, Solid Security Basic, Breadcrumb NavXT, Child Theme Configurator, Classic Editor, Classic Widgets, Custom Sidebars, Duplicate Page, Duplicator, FooBox Image Lightbox, Give – Authorize.net Gateway, Give – Email Reports, Give – Manual Donations, Give – PDF Receipts, Give – Recurring Donations, Give – Tributes, Give – Donation Plugin, Health Check & Troubleshooting, WPCode Lite, MaxButtons, Ninja Forms, Post SMTP, Page Builder by SiteOrigin, Slider by Supsystic, SiteOrigin CSS, SiteOrigin Widgets Bundle, SSL Insecure Content Fixer, Tabs Responsive, Velvet Blues Update URLs, Yoast SEO, WP Rollback, Smush, WP Super Cache, WP Video Lightbox
WordPress wp_mail Owner: /home/sccenter/public_html/wp-content/plugins/post-smtp/Postman/PostmanWpMailBinder.php
WordPress wp_mail Filter(s): wp_staticize_emoji_for_email, PostsmtpMailer->get_mail_args
Postman: 2.8.11
Postman Sender Domain (Envelope|Message): sccenter.org | sccenter.org
Postman Prevent Message Sender Override (Email|Name): No | No
Postman Active Transport: Gmail API (https:login://www.googleapis.com:443)
Postman Active Transport Status (Ready|Connected): Yes | Yes
Postman Deliveries (Success|Fail): 5481 | 10660