More details, from Post SMTP Diagnostic Test
Mailer: postsmtp
cURL Version: 7.68.0
OpenSSL Version: OpenSSL/1.1.1f
OS: Linux 5.4.0-1096-gcp #105-Ubuntu SMP Mon Nov 28 09:19:34 UTC 2022 x86_64
PHP: Linux 8.0.25 C
PHP Dependencies: iconv=Yes, spl_autoload=Yes, openssl=Yes, sockets=Yes, allow_url_fopen=Yes, mcrypt=No, zlib_encode=Yes
WordPress: 6.1.1 en_US UTF-8
WordPress Plugins: Post SMTP, Gravity Perks, Gravity Forms, Advanced Custom Fields PRO, WP Offload Media, Astra Pro, Comment Blacklist Updater, Yoast Duplicate Post, Email Encoder - Protect Email Addresses, FacetWP, GAinWP Google Analytics Integration for WordPress, Lightbox for Gallery & Image Block, Gravity Forms Image Choices, GP Blocklist, Header Footer Code Manager, WPCode Lite, iThemes Security Pro, MainWP Child Reports, MainWP Child, Spectra, User Role Editor, User Switching, Yoast SEO Premium, Yoast SEO, WP Mega Menu, Smush Pro, WPMU DEV Dashboard, WP Pusher
WordPress wp_mail Owner: /www/obfuscated/public/wp-content/plugins/post-smtp/Postman/PostmanWpMailBinder.php
WordPress wp_mail Filter(s): wp_staticize_emoji_for_email, PostsmtpMailer->get_mail_args
Postman: 2.4.1
Postman Sender Domain (Envelope|Message): gmail.com | gmail.com
Postman Prevent Message Sender Override (Email|Name): No | No
Postman Active Transport: SendGrid API (https://api.sendgrid.com:443)
Postman Active Transport Status (Ready|Connected): Yes | Yes
Postman Deliveries (Success|Fail): 5959 | 13