Plugin stopped working

Our Post SMTP plugin mysteriously stopped working right around the time that we changed hosting. We’re having trouble diagnosing the issue ourselves and are hoping that we could get some assistance. Plain english explanations/instructions are greatly appreciated!

Here’s a video that described the issue, as far as I’m capable of seeing: https://share.getcloudapp.com/P8umP7JK

Here is the github page referenced in my video: https://github.com/PHPMailer/PHPMailer/wiki/Troubleshooting

Here is the results of the diagnostic test:
Mailer: phpmailer
HostName: fresnel-prism.com
cURL Version: 7.58.0
OpenSSL Version: OpenSSL/1.1.1
OS: Linux pod-157042 5.4.0-1028-gcp #29~18.04.1-Ubuntu SMP Mon Oct 5 16:41:43 UTC 2020 x86_64
PHP: Linux 7.4.13 C
PHP Dependencies: iconv=Yes, spl_autoload=Yes, openssl=Yes, sockets=Yes, allow_url_fopen=Yes, mcrypt=No, zlib_encode=Yes
WordPress: 5.6 en_US UTF-8
WordPress Theme: Storefront Child
WordPress Plugins: ManageWP – Worker, Advanced Custom Fields PRO, Async JavaScript, Better Search Replace, WordPress Backup & Security Plugin – BlogVault, Classic Editor, Contact Form 7, Custom Related Products for WooCommerce, Google Tag Manager for WordPress, Facebook for WooCommerce, Flamingo, iThemes Security Pro, Jetpack by WordPress.com, Mailchimp for WooCommerce, New User Approve, Post SMTP, Redirection, Advanced Editor Tools (previously TinyMCE Advanced), WooCommerce UPS Shipping Plugin with Print Label, User Role Editor, Video User Manuals, WooCommerce Reviews Manually Approved, WooCommerce Composite Products, WooCommerce Dynamic Pricing, WooCommerce Authorize.Net Gateway, WooCommerce Print Invoices/Packing Lists, WooCommerce USPS Shipping, WooCommerce, WordPress Importer, Yoast SEO, WP Product Feed Manager, WP Sitemap Page, WPMU DEV Dashboard
WordPress wp_mail Owner: /nas/content/live/stagingfresnel/wp-includes/pluggable.php
WordPress wp_mail Filter(s): wp_staticize_emoji_for_email, PostsmtpMailer->get_mail_args
WordPress phpmailer_init Action(s): wpcf7_phpmailer_init, my_phpmailer_example, PostsmtpMailer->phpmailer_smtp_init
Postman: 2.0.16
Postman Sender Domain (Envelope|Message): fresnel-prism.com | fresnel-prism.com
Postman Prevent Message Sender Override (Email|Name): No | No
Postman Active Transport: SMTP (smtp:none:plain://localhost:587)
Postman Active Transport Status (Ready|Connected): Yes | No
Postman Deliveries (Success|Fail): 718 | 75