How to Fix “550 Relay Not Permitted” Error in Emails October 25, 2025

The “550 Relay Not Permitted” error appears when your outgoing mail server cannot verify that you are authorised to send emails. This issue is mainly related to authentication or SMTP configuration settings.

What is the “550 Relay Not Permitted” Error?

This error occurs when your mail server rejects outgoing emails because it believes you are trying to send messages through it without proper authentication or authorisation.
In short: Server says > You are not allowed to send mail through me!
Error variants may look like:

550 Relay not permitted
550 5.7.1 Unable to relay
550 Authentication Required

What Causes This Error?

You may encounter this error if:

• SMTP authentication is disabled.
• Incorrect login credentials are used.
• The wrong server hostname or port is configured.
• The sending IP isn’t allowed by the server.
• SPF or DNS records are misconfigured.

Fixes for the 550 Relay Not Permitted Error

1. Enable SMTP Authentication
   Turn on Outgoing Server Authentication and verify:
   • Username: full email address
   • Password: correct email password
   • Encryption: SSL/TLS or STARTTLS
   • Ports: 465 (SSL) or 587 (TLS)
2. Verify Outgoing Mail Server Address
   Use the correct SMTP credentials provided by your host:
   • Ensure that you are using the correct SMTP credentials provided by your hosting provider.
   • The SMTP host is usually set as yourdomain.com.
   • For secure sending, use port 587 with TLS or 465 with SSL, and make sure SSL/TLS encryption is enabled.
   • Also, avoid using ISP SMTP servers like smtp.gmail.com unless they are properly configured because this can trigger relay issues.
3. Check Sender Email “From” Address
   1. It should be a valid and existing email address.
   2. It must belong to the authenticated mailbox.
   3. It should not contain any spelling mistakes.
      Example:
      Wrong: [email protected]
      Correct:
      [email protected]
4. Verify DNS & MX Records
   1. Run online DNS lookup or CLI:

      nslookup -type=mx yourdomain.com

      Ensure MX records match your hosting server.

5. Check SPF & DKIM Records
   •  Make sure DNS includes an SPF TXT record like:

     v=spf1 a mx include:mailserver.com ~all

     If SPF doesn’t authorise the sending IP > the Mail server blocks it.

6. Check if the Sending IP Is Blocklisted
   • Use tools like:
     MXToolbox Blacklist Check
     Spamhaus
   • If listed > request delisting.
7. Correct Ports / Encryption
   1. Try switching:
      Port 25 > 587 or 465
   2. Encryption None > SSL/TLS
      Some ISPs block port 25 by default.
8. Whitelist or Allow Relay (Server-Side)
   For VPS/Dedicated server environments:
   • Authorise sending IPs in Postfix/Exim
   • Ensure POP before SMTP or SMTP Auth is enabled
     Example for Postfix:

     smtpd_recipient_restrictions =
     permit_sasl_authenticated,
     permit_mynetworks,
     reject_unauth_destination

According to the article above, the “550 Relay Not Permitted” error typically occurs when SMTP settings are incorrect or when authentication is not enabled. Verifying and updating your outgoing mail configuration usually resolves the issue. If the problem persists, contact our support team to help identify and resolve the issue promptly.

Looking to improve your server’s security? Check out our guide on How to configure SSH Key authentication on a remote server