Understanding and Fixing “Error 550 Relay Not Permitted”
If you’re sending emails and encounter the message “550 Relay Not Permitted”, you’re likely dealing with a common email delivery issue that affects servers using the Simple Mail Transfer Protocol (SMTP). This error usually appears when the email server refuses to send a message on behalf of a different domain or unauthorized sender.
The error indicates that your SMTP server is rejecting your attempt to send an email because it thinks you’re trying to relay a message from a third party without permission. Email relaying means sending an email through a mail server that is not responsible for the sender’s or recipient’s domain.
Authentication Failure
You’re trying to send mail without properly logging into the SMTP server.
Misconfigured Email Client Settings
Incorrect SMTP settings (such as the outgoing server, port, or security type) are a frequent cause.
Using the Wrong SMTP Server
Attempting to send mail through a server that doesn’t belong to your domain.
Blacklisted IP or Domain
Some servers block relaying for IPs that are on spam blacklists or have poor reputations.
Blocked Port or ISP Restrictions
Some ISPs block port 25 or restrict mail relaying to fight spam.
Ensure your email client is set to use authentication when sending mail:
In Outlook, Thunderbird, or similar:
Go to Account Settings > Outgoing Server (SMTP)
Enable “My outgoing server (SMTP) requires authentication”
Double-check you’re using the correct outgoing mail server and port:
Common settings:
SMTP server: smtp.yourdomain.com or your provider’s server
Port: 587 (STARTTLS) or 465 (SSL)
Avoid port 25 unless explicitly allowed by your host
Ensure the “From” address matches the domain authorized to send mail through your SMTP server.
Make sure the sending domain is properly configured with:
SPF (Sender Policy Framework)
DKIM (DomainKeys Identified Mail)
DMARC (Domain-based Message Authentication, Reporting, and Conformance)
These help mail servers validate that your domain has permission to send mail.
If you’re running your own mail server:
Check firewall and spam protection rules
Ask your hosting provider or IT admin to allow relay for your IP if authorized
Always use authenticated SMTP when sending mail.
Avoid open relays — these are exploited by spammers and can get your server blacklisted.
Regularly monitor your IP reputation and domain DNS records.
or
If the error persists after correcting the settings, contact your email hosting provider with:
The full error message
A sample email header
Your IP address and domain name
They can assist in verifying authentication logs and server policies.
“550 Relay Not Permitted” is a common SMTP error, but one that’s easy to fix with the right configuration and authentication. Proper email client setup and valid DNS records are the key to smooth email delivery and avoiding relay issues.