Why are my emails being rejected by bb.go.th and marked as spam?
Michael Ko
Co-founder & CEO, Suped
Published 9 Aug 2025
Updated 18 Aug 2025
9 min read
Getting your emails rejected, especially by a domain like bb.go.th, can be incredibly frustrating, particularly when the bounce message simply states your email was detected as spam. I've seen this specific error, 554 5.7.1 This email from IP <> has been rejected. The email message was detected as spam., many times, and it points to a problem beyond a simple IP blocklist (or blacklist) entry. This type of rejection usually signifies an issue with your email's content or your overall sending practices, which are triggering the recipient's spam filters.
The key here is that the message explicitly states the email message was detected as spam, rather than citing an IP address or domain on a publicly known blocklist. This means bb.go.th's email security gateway, likely a Fortinet system given the error signature, is scrutinizing the actual content of your message.
Resolving this requires a multi-faceted approach, diving deep into your email's technical configuration, content, and sender reputation. It's not just about getting off a blacklist; it's about proving your legitimacy to sophisticated spam filtering systems. This guide will help you understand why your emails are facing these rejections and provide actionable steps to get your messages delivered.
Deciphering the 554 5.7.1 rejection code
When you encounter a 554 5.7.1 rejection, it's a generic transaction failed error that typically signifies a permanent failure due to policy reasons. In the context of bb.go.th marking your emails as spam, it means their mail server has evaluated your message and decided it doesn't meet their security criteria. This often happens even before the email fully enters the recipient's inbox queue.
Many email providers, including government domains like bb.go.th, employ stringent spam filtering to protect their users. These filters are constantly updated and can be highly sensitive. As highlighted by some community discussions, even minor tweaks to a spam filter's aggressiveness can lead to widespread rejections for legitimate senders. You can find related conversations on why emails are rejected as spam on Microsoft's answers forum.
The lack of an explicit blocklist (or blacklist) mention in the error message is a strong indicator that the rejection isn't due to your IP or domain being listed on a public real-time blocklist (RBL). While checking blocklists is always a good practice, in this specific case, the focus should shift towards what's inside your email and your overall sending reputation. If you're encountering rejections from Gmail or Outlook/Hotmail, the underlying issues are often similar, revolving around content and sender reputation.
Understanding the 554 5.7.1 error
This SMTP error code indicates a permanent failure related to a policy violation or spam detection by the recipient server. It's often the final stage of the SMTP conversation where the recipient server explicitly rejects the message. Unlike temporary errors, this means the server has made a definitive decision that your email is unwelcome.
Common causes for emails flagged as spam
When emails are flagged as spam due to content, various elements within your message could be the culprit. Spam filters, including those potentially used by bb.go.th, analyze everything from your subject line to the links embedded in your email. One common trigger is the use of suspicious links, like shorteners, which spam filters often flag. Postmark's blog highlights this issue, noting how link shorteners can lead to blocking.
The content-based rejection suggests that the specific Fortinet email security gateway identified in the Slack thread might be leveraging its web filtering capabilities. You should check if any URLs in your messages are listed as malicious on the Fortiguard webfilter site. Even without explicit listing, certain content patterns, such as excessive use of bold text, all caps, or certain keywords, can increase your spam score. Poor formatting, broken HTML, or a high image-to-text ratio can also raise red flags.
Beyond the immediate content, your sender reputation plays a massive role. If you have a history of sending to inactive addresses, getting spam complaints, or sending unauthenticated emails, your domain's reputation suffers. This can lead to your emails being marked as spam even if the current message content appears benign. You might be interested in our guide on why emails are marked as spam even with good domain reputation, as it delves deeper into these hidden factors.
Content Element
Spam Risk Indicator
Best Practice
Links
Excessive or suspicious links, link shorteners, malicious URLs (check Fortiguard).
Use full, reputable URLs. Ensure linked content is safe.
Keywords
Spam trigger words (e.g., "free money," "guaranteed"), all caps, excessive exclamation marks.
Write naturally and avoid salesy, aggressive language.
Formatting
Poor HTML, single large images, low text-to-image ratio, embedded forms.
Use clean HTML, balance text and images, avoid complex elements.
Attachments
Executable files, large file sizes, unusual file types.
Only send necessary attachments, use common file types, keep size small.
Ensuring proper email authentication
Even if your IP isn't on a public blocklist, solid email authentication is non-negotiable for deliverability. SPF, DKIM, and DMARC records are the foundational elements that prove your emails are legitimate and haven't been tampered with. ISPs rely heavily on these to verify sender identity. If these records are misconfigured or missing, even perfect content can be flagged as suspicious.
SPF (Sender Policy Framework) specifies which mail servers are authorized to send email on behalf of your domain. DKIM (DomainKeys Identified Mail) provides a way to digitally sign your emails, allowing the recipient server to verify that the email hasn't been altered in transit. DMARC (Domain-based Message Authentication, Reporting, and Conformance) brings SPF and DKIM together, providing instructions to recipient servers on how to handle emails that fail authentication checks, and providing reporting. You can learn more about DMARC, SPF, and DKIM in our comprehensive guide.
For bb.go.th, or any recipient, if your authentication fails, it's a huge red flag. Even if the spam filter doesn't explicitly state DMARC failed, it contributes to a lower sender score and makes your emails more likely to be marked as spam. Regularly reviewing your DMARC reports (especially from Google and Yahoo) can provide valuable insights into any authentication failures your domain might be experiencing, which could be affecting delivery to other domains as well. This information can help you troubleshoot why your messages are failing authentication and how to fix common DMARC issues.
This record sets your policy to p=none, meaning no action is taken on failed emails, but you receive reports. This is a good starting point for gathering data without impacting deliverability while you identify issues.
Steps to improve deliverability to bb.go.th
Since the rejection is content-based, the first step is to thoroughly review your email's content. Look for common spam triggers like excessive capitalization, unusual fonts, too many images, or suspicious phrases. Ensure all links are reputable and fully spelled out. If you're using a link shortener, try sending an email without it as a test. Consider running your email through an email deliverability tester to get insights on potential spam scores.
Your sender reputation is paramount. If you've had issues with emails being blocked by Bigpond or landing in Yahoo spam, these could be symptoms of a broader reputation problem. Ensure your email lists are clean and regularly updated to remove inactive or invalid addresses. High bounce rates and spam complaints significantly damage your standing with ISPs. Our article on why your emails go to spam can offer further insights.
Contact the recipient: If possible, reach out to the recipient's IT department or postmaster (for bb.go.th, this might be challenging but worth trying) to inquire about their specific email policies or to whitelist your sending domain.
Review your IP/domain health: Use a blocklist checker to ensure your IP and domain are clear, even if not explicitly mentioned in the bounce. A poor reputation from past issues can linger.
Implement strong authentication: Ensure your SPF, DKIM, and DMARC records are correctly configured and aligned. This builds trust with recipient servers, making your emails less likely to be considered spam.
Warm up new IPs/domains: If you're using new sending infrastructure, gradually increase your sending volume to build a positive sending history.
Monitor deliverability: Continuously track your email performance, including bounce rates, spam complaint rates, and inbox placement. This allows you to quickly identify and address issues. For more technical solutions, review our article on technical solutions from top performing senders.
Navigating email rejections
Overcoming email rejections, especially those tied to content-based spam filtering, requires diligence and a proactive approach. It's not always about a single issue, but often a combination of factors that collectively lower your sender score in the eyes of an ISP's spam filters.
By meticulously reviewing your email content, ensuring robust authentication, and maintaining a stellar sender reputation, you can significantly improve your chances of reaching the inbox at domains like bb.go.th. Remember, consistent positive sending behavior is the best way to build and maintain trust with mail servers worldwide.
Views from the trenches
Best practices
Always include a plain-text version of your email to ensure compatibility and accessibility.
Segment your audience and tailor content to avoid generic, spammy-looking messages.
Actively monitor your sender reputation and DMARC reports for early warning signs.
Common pitfalls
Ignoring bounce messages and not analyzing the rejection codes for clues.
Using generic subject lines or email templates without personalization.
Sending emails to old, unengaged, or unverified email addresses.
Expert tips
Test emails on various clients and spam checkers before large sends.
Maintain consistent sending volume to avoid sudden spikes that trigger filters.
Engage with recipients to build a positive sending history and encourage whitelisting.
Marketer view
Marketer from Email Geeks says they had a similar issue where an IP was being rejected and the error message didn't specify an RBL, suggesting it could be an internal block.
2021-01-25 - Email Geeks
Expert view
Expert from Email Geeks says the 554 5.7.1 response indicates the message content was the issue, not necessarily the IP. They suggested confirming the stage at which this response was received.
(especially from Google and Yahoo) can provide valuable insights into any authentication failures your domain might be experiencing, which could be affecting delivery to other domains as well. This information can help you troubleshoot why your messages are failing authentication and how to fix common DMARC issues.
