SMTP Error: Could not authenticate.

Plugin Support


Hi @chrdol72

Thanks for reaching out and we’re sorry to hear that you’re experiencing issues with the Other SMTP mailer.

I looked through the log that you shared and I noticed these reasons:

  • “Could not authenticate.”
  • “We do not authorize the use of this system to transport unsolicited, 220, and/or bulk e-mail.”
  • Password command failed: 535 Incorrect authentication data

These SMTP errors indicate that your web server isn’t able to connect to the SMTP server.

Please, recheck your SMTP credentials with your SMTP provider.

Also, there could be a firewall between your web server and the SMTP server. When you get a chance, could you please contact your web hosting support and ask them to look into the issue? You can provide them with the SMTP settings you’re using and this SMTP log. They should be able to figure out the issue.

Alternatively, we recommend setting up other available mailers instead of using “Other SMTP”. The “Other SMTP” mailer does not use a dedicated API, which can lead to potential errors based on your website hosting settings.

Transactional Mailers

Transactional email service providers such as our #1 recommended mailer, SendLayer (, are perfect for sending emails from your WordPress site. If it’s contact form notifications or e-commerce emails, they will deliver them quickly and reliably. 

Sendinblue,, SendGrid, and Mailgun are also transactional email service providers if you’d like to consider your options.

Transactional mailers also allow you to send emails with custom ‘From Email’ specific to your domain (examples:,

If you’d like to check out more details on the mailers mentioned above or any others you may be interested in, you can see our complete guide here:

I hope this helps 🙂


This site will teach you how to build a WordPress website for beginners. We will cover everything from installing WordPress to adding pages, posts, and images to your site. You will learn how to customize your site with themes and plugins, as well as how to market your site online.

Buy WordPress Transfer