How to avoid MailChannels errors

As you’re probably aware, hosting companies relay millions of emails every day on behalf of their customers and employ sophisticated tools to ensure secure and reliable delivery. At HostPapa, a service called MailChannels automatically detects and blocks the sending of spam, phishing and other abusive types of email.

If you receive an error when attempting to send an email, it may be because it has been identified as a risk (correctly or sometimes incorrectly) by MailChannels. In cases like these, the email(s) are not sent to the recipient, and the sender receives an error message.

There are numerous reasons why MailChannels may flag an email as a risk. A common issue is the use of subject lines that are found in widespread spam campaigns, for example, variations of greetings such as re: fwd: hello, hi, etc.

Understanding MailChannels errors

If you received a “bounced” email message, check the email headers for an error code.

Email error code

You may also find a link following this code that can be followed to understand more about the problem. 

Diagnosing the error message received is the first step to resolving the issue identified and ensuring your email is safely received. Let’s look at some common error messages and steps you can take to resolve them.

550 5.7.1 [SS] error

The 550 5.7.1 [SS] error indicates that the subject line in the message contains one or multiple spam-like keywords commonly used on abusive or unsolicited email. These can include pharmaceutical terms and/or prescription medication names, lewd or obscene references, and other firm indicators of unsolicited or unwanted message traffic.

550 5.7.1 [RBL] Sender blocked <IP or domain> error

If you’re receiving this error, it means your email message was sent from a server or domain that is currently listed as a high-volume spam source by a reputable global black list.

First, check the IP address or domain listed in the error message against reputable black lists:

If the domain is blacklisted, follow the steps below to ensure your account is not compromised, then contact Spamhaus to request that they delist the domain.

If the IP address is blacklisted, please contact HostPapa Support.

550 5.7.1 [CS] message blocked. error

Messages returned with this error have been positively identified as spam. Check the email details and, if you believe this error to be a “false positive”, contact HostPapa Support with the details presented in the Resolving False positive section below to request the email is not blocked.

550 5.7.1 [IRR] error

This error indicates that the email account has been blocked because the account has been sending emails to a large number of invalid addresses. Spammers often send to a large number of invalid recipients. A high number of invalid recipients will harm the IP reputation.

In this case, check and clean your mailing list, removing any invalid email addresses. You can use a website such as or for address verification.

Other tips include:

  1. Reduce the number of invalid recipients on your list by using double opt in (includes confirmation).
  2. Remove invalid recipients from your list immediately. You will always have some invalid addresses due to people changing email addresses, but the lower the number, the better your reputation.
  3. Only send to subscribers who have opted in to your list. Your contacts must subscribe to your emails and have valid email addresses. If they don’t and then mark your email as spam and we receive a feedback complaint, your account will get suspended temporarily or permanently.

Once your mailing list is cleaned and the number of invalid addresses is reduced, you will be able to send mails automatically without any intervention.

550 5.7.1 [FBL] error

This error indicates that a previous recipient has made a complaint about email originating from your IP address or account. In keeping with email sender best practices, MailChannels automatically blocks senders who receive complaints.

Sometimes, these complaints can be sent by mistake by users hitting a Spam Report button by mistake. Others may identify an email as spam, rather than simply deleting the email. MailChannels cannot reveal the identity of the complainant – doing so would enable spammers to fine tune or “wash” their recipient lists to avoid future detection.

Tips to avoid spam complaints include:

  • Only sending email messages that recipients could reasonably expect to receive;
  • Not surprising recipients with new messages after many months of zero contact;
  • Keeping the purpose of your communication as clear as possible; and,
  • Providing unsubscribe links prominently at the top AND bottom of each message.

The MailChannels system uses an adaptive approach for blocking senders that receive complaints. Once the level of complaints drops back to an acceptable level, the sender will no longer be blocked.

550 5.7.1 [ESA] sender blocked error

This error indicates that extensive abuse has been indicated, originating from your email account. Examples of abuse include:

  • Spam email
  • Bulk email
  • High complaint rates
  • Lots of invalid recipients

The MailChannels system automatically implements temporary blocks on abusive accounts. After a number of these temporary blocks have been issued and the system continues to see the problematic traffic, a permanent block is issued which must be manually removed in order to continue sending/relaying through the MailChannels systems.

If you experience this error, first, follow the steps below to secure your account. Once complete, follow the link included with the bounced error message to unblock the account. If the account is unblocked without your account being secured it will get blocked again. An account can be unblocked without any manual intervention only once every 30 days.

5.7.1 [CSR] account blocked error

If you see this error, it means the email account has been blocked because it has been sending a high volume of spam. It’s likely that your account has been compromised.

Follow the Securing you account steps below. The system will automatically remove the block once spamming stops. No manual intervention is required to unblock the account.

Resolving false positives

If you feel that the rejection is a “false positive”, please open a support ticket from your HostPapa Dashboard and include the following details:

  1. Sender email address
  2. Subject
  3. Recipient email address
  4. Date & Time

Securing your account

If you are receiving email rejection notifications on a regular basis, particularly for emails that you do not recognize, it’s possible that your account may be compromised.

Secure your account with the following steps:

  • Change your password. Ensure your new password has a minimum length of eight characters and uses a mixture of upper and lower case letters, numbers, and special characters.
  • Verify that your operating system is running with the latest security updates.
  • Update your anti-virus software and conduct a full scan of your system to ensure that a spammer has not installed spam-sending malware on your computer.

If you continue to receive errors, please contact HostPapa Support to discuss the issue.

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