SMTP Authentication Fails with App Password – “535 Authentication Failed” Error

SMTP Authentication Fails with App Password – “535 Authentication Failed” Error

Hello,

I'm trying to send transactional emails from my WordPress website using the WP Mail SMTP plugin with Zoho Mail (smtp.zoho.com on port 465 with SSL).

I've created and used a Zoho Mail app-specific password for SMTP, and verified that:

  • The email and password are correct

  • SMTP is enabled on my account

  • I'm connecting via ssl://smtp.zoho.com:465

  • I tried forcing the authentication method to LOGIN (as per PHPMailer recommendations)

  • I’ve tested from multiple accounts using the same domain

Despite all of this, I keep getting this error in the logs:

SMTP INBOUND: "535 Authentication Failed"
SMTP ERROR: Password command failed: 535 Authentication Failed
SMTP Error: Could not authenticate.

Can you please help me:

  • Confirm that SMTP access is properly enabled for my domain/account

  • Verify if there’s any server-side issue with authentication or blocked connection

  • Ensure that my Zoho Mail account allows external SMTP clients (like WP Mail SMTP) to authenticate and send emails

Thank you!