5.5.1 authorization failed

Hi there,

Since november 2021 on one of our clients site Postman SMTP suddenly stopped working. It gives the error ‘5.5.1 authorization failed’, even though nothing is changed and our client is 100% sure all the information they put in is correct.

What can the problem be? Is the problem at the domainname host or the webhost?

I’ll post the diagnostic info here as well:

Mailer: postsmtp
HostName: despreng-academie.nl
cURL Version: 7.66.0
OpenSSL Version: OpenSSL/1.1.1l-fips
OS: Linux c70886.sgvps.net 3.12.18-clouder0 #1 SMP PREEMPT Wed Jun 9 16:10:01 EEST 2021 x86_64
PHP: Linux 7.4.28 C
PHP Dependencies: iconv=Yes, spl_autoload=Yes, openssl=Yes, sockets=Yes, allow_url_fopen=Yes, mcrypt=No, zlib_encode=Yes
WordPress: 5.9.1 nl_NL UTF-8
WordPress Theme: FlowAcademy Theme
WordPress Plugins: Gravity Forms, Admin Page Spider Pro Pack, Astra Pro, Beaver Builder Plugin (Agency Version), Beaver Themer, Ultimate Addons for Beaver Builder, PowerPack for Beaver Builder, Better Search Replace, Beaver Team Pro, CartFlows Pro, CartFlows, Complianz Privacy Suite (GDPR/CCPA) premium, Gravity Forms Mailchimp Add-On, Imsanity, iThemes Security Pro, LifterLMS Helper, LifterLMS WooCommerce, LifterLMS Labs, LifterLMS, Loco Translate, LoginPress - Auto Login, LoginPress Pro, LoginPress - Customizing the WordPress Login Screen., MainWP Child, Mollie Payments for WooCommerce, Post SMTP, SiteGround Optimizer, ShortPixel Image Optimizer, UpdraftPlus - Backup/Restore, User Role Editor Pro, WC-AC Hook, WooCommerce PDF Invoices & Packing Slips, WooCommerce Subscriptions, WooCommerce, WP Fusion, WP Rocket, WP Rollback, SEOPress PRO, SEOPress
WordPress wp_mail Owner: /home/customer/www/despreng-academie.nl/public_html/wp-content/plugins/post-smtp/Postman/PostmanWpMailBinder.php
WordPress wp_mail Filter(s): wp_staticize_emoji_for_email, WPO\WC\PDF_Invoices\Main->set_phpmailer_validator, PostsmtpMailer->get_mail_args
WordPress phpmailer_init Action(s): PostsmtpMailer->phpmailer_smtp_init
Postman: 2.0.24
Postman Sender Domain (Envelope|Message): centrumdespreng.nl | centrumdespreng.nl
Postman Prevent Message Sender Override (Email|Name): No | No
Postman Active Transport: SMTP (smtp:tls:plain://web1.jointartistic.com:25)
Postman Active Transport Status (Ready|Connected): Yes | Yes
Postman Deliveries (Success|Fail): 781 | 449

Thanks in advance!