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 Email sending error - 550 Please turn on SMTP Authentication
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Email sending error - 550 Please turn on SMTP Authentication

This guide explains what causes the “Email Sending Error 550 – Please turn on SMTP Authentication” and why it occurs. By following the steps in this guide, you’ll learn how to enable SMTP authentication and send emails successfully again.

 

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  • Email client (desktop, mobile, or browser)

 

 

Issue

Users are unable to send emails and receive an error or bounceback message similar to the following:

550 Please turn on SMTP Authentication in your mail client..... is not permitted to relay through this server without authentication.

 

Cause

The outgoing SMTP authentication failed because:

  • SMTP username/password is missing or incorrect
  • SMTP port is wrong (should be 465 SSL or 587 TLS, never port 25)
  • Gmail → Send mail as → uses wrong credentials
  • Your SMTP server requires authentication per RFC rules
  • The mail server doesn't allow sending from your current IP without login

It has NOTHING to do with SPF, DKIM, or the recipient.

 

1. Gmail accepted your draft → tried to send → handed off to your SMTP server

You are using Gmail to send mail from a non-Gmail domain (via “Send mail as”, SMTP settings).

2. Your external SMTP server rejected the email

It rejected it for one specific reason:

550 Please turn on SMTP Authentication in your mail client..... is not permitted to relay through this server without authentication.

This means your SMTP server said:

“You’re trying to send through me BUT you didn’t authenticate properly.”

3. Gmail interpreted the rejection as “misconfigured server”

So, Gmail added the generic statement:

“the remote server is misconfigured.”

Even though the real issue is incorrect SMTP authentication, not server misconfiguration.

 

Solution

If you are sending through Gmail "Send mail as":

  1. Go to Gmail → Settings (gear) → See all settings
  2. Go to Accounts and Import
  3. Under Send mail as, click edit info
  4. Re-enter the correct SMTP settings:
    • SMTP server: mail.(yourdomain.com)
    • Port: 465 (SSL) or 587 (TLS)
    • Username: full email address
    • Password: email password
  5. Make sure SMTP Authentication is ON
  6. Save changes


If sending through Outlook, Apple Mail, Thunderbird, or mobile:

  • Enable Outgoing SMTP Authentication
  • Use the same username & password as incoming mail
  • Use port 465 + SSL or 587 + TLS


For cPanel email, please check the cPanel troubleshooting steps

 

 

 

 

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