MailChannels is an email relay service designed to prevent spam and improve email deliverability. However, when sending emails through MailChannels, users may occasionally receive error messages that prevent successful delivery. These errors often indicate spam-like activity, authentication issues, or problems with the recipient’s address.

If you receive an error when trying to send an email, you can use the MailChannels Insights Dashboard to review your outgoing mail logs. This dashboard provides detailed information about the emails you send, including error messages and delivery issues. Checking these logs can help you quickly diagnose and resolve sending errors.

In this guide, we’ll explain the most common MailChannels sending errors, their causes, and how to fix them.

550 5.7.1 [CS] – Message Blocked (Spam Detected)

Error Message:

550 5.7.1 [CS] Message blocked Spam

Cause:

• The email was flagged as spam by MailChannels.
• The content includes spam-like keywords (e.g., pharmaceutical terms or misleading subject lines).

How to Fix It:

• If you believe this is a false positive, see our Reporting False Positives in MailChannels article.
• Avoid common spam triggers, such as misleading subject lines or excessive links and images.
• Ensure your emails follow best practices for legitimate email sending.

550 5.7.1 [ESA] – Sender Blocked (Abuse Detected)

Error Message:

550 5.7.1 [ESA] Sender blocked error

Cause:

• High volume of spam, bulk emails, or excessive complaints from recipients.
• Sending emails to many invalid recipients.

How to Fix It:

• Change your email account password to prevent unauthorized access.
• Run a full anti-virus scan on your computer to detect malware.
• Ensure your email list contains only valid, opted-in recipients.
• Follow the instructions in the bounced email to request unblocking.

550 5.7.1 [RBL] – Sender Blocked (Blacklisted IP or Domain)

Error Message:

550 5.7.1 [RBL] Sender blocked

Cause:

• Spam-tracking services like Spamhaus blacklist the sending IP or domain.
• A high volume of emails flagged as spam has resulted in an automatic blacklist.

How to Fix It:

• Check your IP/domain status using tools like MXToolbox or Spamhaus.
• If your domain is blacklisted, follow the delisting instructions on the blacklist’s website.
• Contact us for further assistance.

550 5.7.1 [IRR] – Too Many Invalid Addresses

Error Message:

550 5.7.1 [IRR] error – large number of invalid addresses

Cause:

• Your account has been sending emails to a large number of invalid or non-existent addresses.
• Spammers often send mass emails to invalid recipients, which can damage your sender reputation.

How to Fix It:

• Clean your mailing list using tools like Verify Email Address or Mail Tester.
• Use double opt-in for email signups to ensure valid addresses.
• Remove invalid email addresses from your list immediately.

550 5.7.1 [HIC] – Abuse Detected (Compromised Account)

Error Message:

550 5.7.1 [HIC] error – Abuse

Cause:

• The account has been compromised and is sending spam.

How to Fix It:

• Change your email account and cPanel password immediately.
• Update your computer’s security software and run a full malware scan.
• Ensure your operating system is up to date with security patches.

550 5.7.1 [FBL] – Complaint-Based Block

Error Message:

550 5.7.1 [FBL] error – Feedback Loop Complaint

Cause:

• Recipients have reported your email as spam.
• High complaint rates trigger automatic blocking by MailChannels.

How to Fix It:

• Only send emails to recipients who have opted in.
• Keep email content relevant and avoid sending unexpected messages.
• Provide a clear unsubscribe link at the top and bottom of emails.
• Once complaint rates decrease, MailChannels will automatically remove the block.

550 5.7.1 [SS] – Spam-Like Subject Line

Error Message:

550 5.7.1 [SS] error

Cause:

• The subject line contains keywords commonly associated with spam (e.g., “Re: Hello,” “Congratulations,” “Free,” or “Urgent”).

How to Fix It:

• Avoid using generic or suspicious subject lines.
• Ensure your subject line is clear, relevant, and professional.
• If you believe this is a false positive, see our Reporting False Positives in MailChannels article.

5.7.1 [CSR] – Account Blocked Due to Spam

Error Message:

5.7.1 [CSR] account blocked

Cause:

• A high volume of spam has been sent from the account, leading to an automatic block.

How to Fix It:

• Follow the securing your account steps below.
• The system will automatically unblock the account once the spam stops.

Final Thoughts

MailChannels errors help prevent spam and ensure reliable email delivery. However, if your emails are getting blocked incorrectly, reviewing the MailChannels Insights Dashboard and checking the error codes can help you quickly diagnose and resolve the issue.

If you continue to experience problems, contact us for assistance. Following email best practices and maintaining a clean sender reputation can minimize MailChannels sending errors and ensure smooth email communication.