Why are transactional emails bouncing with 'MailBlockKnownSpammer' and how to resolve it?

Email marketer from Reddit r/emailmarketing suggests that the issue might be related to a recent campaign that triggered spam filters. They recommend segmenting your list and sending more targeted emails to improve engagement and avoid being flagged as a spammer. Also warming up your IP address if you are new to sending volume.

Email marketer from StackExchange answers that a 'MailBlockKnownSpammer' error often means your IP or domain is on a Real-time Blackhole List (RBL). They suggest checking your IP against common RBLs using a tool like MultiRBL and taking steps to get delisted if necessary. Also monitor complaints.

Email marketer from SparkPost Help Center suggests that a possible cause is a sudden increase in email volume. When sending transactional emails, you should follow a schedule of slowly increasing the volumes you send to avoid MailBlockKnownSpammer. They advise to warm up your IP if you have started using a new IP address.

Email marketer from Quora User answers that it could be due to the content of your email. If your email is being flagged as spam, it could be that you have used spam trigger words. Avoid language that might be seen as overly aggressive or promotional.

Email marketer from Litmus Blog stresses the necessity of implementing email authentication protocols like SPF, DKIM, and DMARC. These protocols verify the sender's identity and help prevent spoofing, improving deliverability and reducing the risk of being flagged as a spammer. They recommend regularly checking DMARC reporting.

Email marketer from Postmark Help Center answers that the 'MailBlockKnownSpammer' error often arises because the recipient server identifies the sender as a source of unsolicited email. It advises to check sender reputation through tools like Sender Score, maintain a clean email list (removing inactive or invalid addresses), and monitor feedback loops to address complaints promptly.

Email marketer from EmailonAcid Blog emphasizes the importance of separating transactional and marketing emails onto different IP addresses. This helps maintain the reputation of the transactional IP, ensuring critical messages are delivered reliably. This is important because transactional email should always arrive.

Email marketer from SendGrid Help Center shares that this bounce reason typically means the receiving mail server has blocked the sending server due to perceived spam activity. Suggested actions include verifying your sending reputation, ensuring your emails comply with anti-spam laws (like CAN-SPAM), and contacting the recipient's email provider to request delisting.

Marketer from Email Geeks suggests that the issue might be a smaller security filter or local provider blocking the emails. They advise doing an MX lookup of the domains to identify a common source for remediation.

Email marketer from Mailgun Help Center explains that a 'MailBlockKnownSpammer' bounce indicates the recipient's mail server believes the sending IP address or domain has a history of sending spam. This can happen due to poor sending practices, low engagement, or being listed on blocklists. They recommend checking IP/domain reputation, ensuring proper authentication (SPF, DKIM, DMARC), and improving engagement rates.

Marketer from Email Geeks mentions that Office365 has its own delist submission portal to check if an IP is blocked and request unblocking and provides the link. They also highlight that sending marketing emails from the same IP as transactional emails can cause deliverability problems. They believe someone marked a survey email as spam.

Expert from Spam Resource explains that the 'MailBlockKnownSpammer' message indicates a block based on the sender's perceived reputation. Immediate steps involve checking blocklist status and contacting the blocking entity (e.g., the specific ISP or email provider) for remediation, emphasizing adherence to best practices.

Expert from Word to the Wise emphasizes that consistent and positive sender reputation is vital for transactional email deliverability. She advises monitoring sender reputation using available tools, proactively addressing any negative feedback or complaints, and ensuring clear communication with recipients about the purpose and value of transactional messages.

Documentation from Google Postmaster Tools explains that Gmail uses various signals to identify spam, including user reports, engagement metrics, and sender reputation. To avoid being marked as a spammer, it is crucial to follow Gmail's bulk sender guidelines, which include authenticating emails, maintaining low spam complaint rates, and providing easy unsubscribe options.

Documentation from RFC Editor details that specific SMTP error codes related to blocking (though not explicitly 'MailBlockKnownSpammer') indicate a policy rejection by the receiving server. This means the server has a reason to refuse the message, whether it is due to sender reputation, content filtering, or other security measures. Review your logs to get the exact code that indicates the policy rejection.

Documentation from Microsoft Docs explains that Outlook.com may block senders based on various factors, including spam complaints, high bounce rates, or detection of suspicious sending patterns. It recommends using the Smart Network Data Services (SNDS) and Junk Email Reporting Program (JMRP) to monitor IP reputation and subscriber complaints.