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.

“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: The mail client settings should be properly configured with mail account details, SMTP server, and port number. Furthermore, for PHP mail forms, using SMTP authentication to send out mail can help resolve this error.

To resolve mail server configuration errors, we examine the mail logs, MX records, and related configuration files, and fix the discrepancies that are found in them.

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: Once blacklisted, getting de-listed is a time-consuming procedure. Pinpointing the source of spam and fixing it is the most important step. Then you need to request RBL to remove you from the list.

Then, to ensure seamless mail delivery, it is important to avoid getting blacklisted. At Bobcares, we proactively secure the mail server and keep a constant vigil on them to avoid all spamming activities that can cause the server to get blacklisted.

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: Setting RDNS records for the sending mail server helps to avoid such errors. At Bobcares, we configure critical mail records such as RDNS, SPF, DKIM, etc to ensure that mail delivery errors are avoided.

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: The MX records of the recipient domain should be tested and confirmed to be working fine. To resolve issues at the recipient end, you need to contact the remote mail server with these inputs.

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. The sender’s email account doesn’t exist or cannot be detected
d. Permission issues caused by server migrations, updates, or custom scripts

Fix: To resolve sender errors, we examine the mail server logs, sender email account settings, folder permissions, mail server configuration, etc., and resolve any issues related to that.

At Bobcares, our custom checklists for migrations and updates enable us to avoid any related issues that may pop up. We also audit the mail server settings periodically and reconfigure the ‘Email Routing’ as appropriate.

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.