One commonly encountered email error is “SMTP error from the remote mail server after RCPT TO”. It shows up when users try to send emails to other email accounts.

Email errors can be really bothersome – they can hit you hard and unexpectedly when you attempt to send an urgent mail.

As part of our Server Support services for web hosting providers, we resolve email errors faced by website owners.

About “SMTP error from remote mail server after RCPT TO”

This error message is a very confusing one, as it can be triggered due to a number of causes. But usually, the bounce message that arrives contains the details about the error.

The RCPT command is used to tell the sender mail server, who the recipient of your message is. The error message denotes that the sending mail server faced an error during that command while trying to send mail.

Then, we have to examine the entire bounce message to understand the error. Here are some of the major causes we’ve identified.

An Overview:

• Impacts of the Error
• “SMTP error from remote mail server after RCPT TO” – Causes & Fixes
• 1. Configuration errors
• 2. Domain blacklists
• 3. RDNS misconfiguration
• 4. Recipient errors
• 5. Sender errors
• 6. Syntax Errors in Email Addresses
• 7. Security Restrictions (SPF/DKIM Issues)
• Prevention Measures

Impacts of the Error

 

• Emails may not reach their intended recipients, leading to communication breakdowns.
• Critical messages, especially in professional settings, may not be delivered, resulting in missed deadlines or opportunities.
• Businesses relying on email for operations may face interruptions, affecting productivity and customer relations.

“SMTP error from remote mail server after RCPT TO” – Causes & Fixes

1. Configuration errors

SMTP error from remote mail server after RCPT TO:<user@domain.com>:
host domain.com [xx.xx.xx.xx]: 550-Please turn on SMTP Authentication in your mail client.
550-(host.domain.com) [yy.yy.yy.yy]: __ is not permitted to relay through this server without authentication.

Cause: The authentication errors mostly occur due to mail client or mail form configuration settings. If you try to send mail without proper authentication of your mail account, the mail server throws this error.

Additionally, the authentication error also occurs when there is any mail server configuration issue – like domain not present in localdomains file or MX record mismatches.

Fix:

1. First, check mail client settings bu heading to the email client.
2. Then, go to the account settings.
3. Now, make sure the following details are correct:
   • SMTP Server Address: This should match the email provider’s specifications.
   • Port Number: Common ports are 25, 465 (SSL), or 587 (TLS).
   • Encryption Method: Verify if SSL/TLS is required and enabled.
4. Then, we have to enable SMTP Authentication. So go to the account settings and look for an option like “My outgoing server (SMTP) requires authentication.”
5. Now, make sure this option is checked and that we have entered the correct username and password.
6. For PHP Mail Forms, use a library like PHPMailer or SwiftMailer that supports SMTP authentication. We can configure it to use our SMTP server credentials.

2. Domain blacklists

SMTP error from remote mail server after RCPT TO:<user@domain.com>:
host domain.com [xx.xx.xx.xx]: 550-"JunkMail rejected - host.domain.com [yy.yy.yy.yy]: 
___ is in an RBL, see http://www.spamhaus.org/query/bl?ip=________"

SMTP error from remote mail server after RCPT TO:: host host.domain.com [xx.xx.xx.xx]: 
554 5.7.1 Service unavailable; Client host [yy.yy.yy.yy] blocked using zen.spamhaus.org; http://www.spamhaus.org

Cause: RBLs aka blacklists are used by mail servers to prevent inbound spamming. When blacklist providers such as Spamhaus suspect your mail server as a spam origin, they will blacklist your server IP.

Getting blacklisted indicates that your server had a spammer or someone who is sending mass emails. Many times, server owners get to know about it only when users complain about mail errors.

Fix:

1. Use tools like MXToolbox or Spamhaus to check if your IP is blacklisted.
2. Review server logs to identify any outgoing spam activity.
3. Also, secure the server by implementing rate limits and using anti-spam measures.
4. Once the source of spam is resolved, follow the delisting procedures provided by the blacklist service (e.g., Spamhaus).

3. RDNS misconfiguration

SMTP error from remote mail server after RCPT TO:<user@domain.com>:
host mx.domain.com [xx.xx.xx.xx]: 554 5.7.1 <unknown[yy.yy.yy.yy]>:
Client host rejected: envelope policy RBL PTRNUL

Cause: RDNS pointer records are used to map IP to the hostname and it helps to validate a server. Furthermore, many mail servers reject incoming mail from servers without proper RDNS records.

Fix:

1. Use a tool like dig or nslookup to verify that your IP address resolves to the correct hostname.

   dig -x our_ip_address
2. Contact the hosting provider or DNS administrator to configure RDNS records correctly.
3. Also, ensure SPF and DKIM records are set up properly to enhance email deliverability.

4. Recipient errors

SMTP error from remote mail server after RCPT TO: <user@domain.com>:
552 5.1.1 <user@domain.com> Mailbox delivery failure policy error

SMTP error from remote mail server after RCPT TO:
550 5.1.1 xxxxxxxx Recipient Suspended (TT999)

SMTP error from remote mail server after RCPT TO:<user@domain.com>:
550 5.1.1 <user@domain.com> Recipient not found.

SMTP error from remote mail server after RCPT TO:<user@domain.com>:
host mx.domain.com [xx.xx.xx.xx]: 550 Requested action not taken: mailbox unavailable

Cause: The mail delivery error ‘SMTP error from remote mail server after RCPT TO:’, can be caused by a range of issues at the recipient mail server.

Furthermore, these include missing or suspended recipient email accounts, incorrect MX records, custom blacklists, or filters configured at the recipient email account, which cause mail to bounce back to the sender.

Fix:

1. First, double-check for typos or errors in the email address being used.
2. Then, use dig to confirm that the recipient’s domain has valid MX records.
   dig recipient_domain MX
3. If issues persist, reach out to the recipient’s email administrator for assistance in resolving any internal issues.

5. Sender errors

SMTP error from remote mail server after RCPT  TO:<user@domain.com>:
host host.domain.com [xx.xx.xx.xx]: 554 5.1.8  <user1@domain1.com>:
Sender address rejected: Domain not found

SMTP error from remote mail server after RCPT TO:<user2@domain2.com>:
host mx.server.com [xxx.xxx.xxx.xxx]: 550-Verification failed for <user1@domain1.com>
550-No Such User Here : Sender verify failed

Cause: A sender error can be caused due to many factors. The main reasons we have seen in our role as Website Support Techs for web hosting companies include:

a. Duplicate sender account present in the recipient server

b. Misconfigured mail configuration settings

c. Also, the sender’s email account doesn’t exist or cannot be detected

d. Permission issues caused by server migrations, updates, or custom scripts

Fix:

1. Ensure that the email account is active and correctly configured in the email client.
2. Confirm that the domain’s DNS settings are correct and that there are no discrepancies in MX records.
3. If we have migrated servers recently, ensure that all permissions and configurations have been correctly set up.

6. Syntax Errors in Email Addresses

Cause:Typos in the recipient’s email address can lead to a “550 5.1.1 User unknown” error.

Fix:

Always double-check for spelling errors in email addresses before sending. Also, use email validation tools to ensure addresses are correctly formatted.

7. Security Restrictions (SPF/DKIM Issues)

Cause: If emails are sent from servers not listed in the SPF record of a domain, they may be rejected as unauthorized.

Fix:

Ensure that the SPF record includes all servers authorized to send emails on behalf of our domain.
Modify application settings (like those in Opencart) to ensure that outgoing emails use a valid sender address that matches your domain.

Preventive Measures

• Implement tools to validate email addresses before sending to catch typos or invalid formats.
• Additionally, ensure that SMTP authentication is enabled in mail clients and that all settings are correctly configured.
• Regularly check and update DNS records, including MX records, SPF, DKIM, and RDNS settings to ensure they are accurate and up-to-date.
• Also, maintain detailed logs of email transactions to quickly identify and troubleshoot issues when they arise.
• Provide training for users on proper email address entry and the importance of checking details before sending emails.
• Furthermore, employ monitoring solutions that alert administrators to delivery failures or changes in email performance metrics.
• Periodically audit email configurations and server settings to identify potential issues before they affect users.

Conclusion

“SMTP error from remote mail server after RCPT TO” error is a common error that affects email delivery. Here we’ve discussed five major causes our Server Support Engineers have seen and how we fix it.