Why are Bigpond emails bouncing with a content-based spam reason?
Michael Ko
Co-founder & CEO, Suped
Published 9 May 2025
Updated 17 Aug 2025
10 min read
Receiving bounce-back messages from Bigpond.com addresses can be a frustrating experience. Especially when the bounce reason explicitly states "Message content rejected due to suspected spam," it points directly to an issue within the email's body or subject line. This type of rejection is distinct from authentication failures or recipient address issues. It tells us that Bigpond's (or Telstra's) spam filters have identified something within your message itself that triggers their detection algorithms.
These content-based rejections are not always permanent. However, they are serious warning signs that require immediate attention to prevent further deliverability problems and potential damage to your sender reputation. A high volume of such bounces can lead to broader blocks, affecting all your emails to Bigpond recipients.
Understanding why this happens and what steps to take is crucial for maintaining good email deliverability. This guide will help you identify common content issues, implement best practices, and work towards resolving these frustrating bounce errors.
Why Bigpond rejects content
When Bigpond rejects an email due to suspected spam content, it means their internal filtering systems have flagged specific elements within your message. These systems are highly sophisticated and constantly updated to combat evolving spam tactics. It's important to remember that even legitimate marketing or transactional emails can inadvertently trigger these filters if they resemble known spam patterns.
One common cause is the use of certain keywords or phrases that are frequently associated with spam. This includes excessive use of promotional language, urgent calls to action, or words related to finance, pharmaceuticals, or illicit activities. Spam filters also scrutinize the email's formatting, such as overly large fonts, too many images, or a poor text-to-image ratio. Sometimes, even seemingly innocent elements like emojis in the subject line or body can contribute to a higher spam score, although Bigpond's policies on emojis specifically are not as widely known as those of some other providers.
Beyond explicit spammy content, other factors can make your email appear suspicious. Links to untrusted domains, shortened URLs, or an unusually high number of links within the email can raise red flags. Additionally, if your email includes attachments that are commonly used in phishing attempts (e.g., executables, ZIP files), even if benign, they can lead to content-based rejections. It's a cumulative score, and a combination of several minor issues can tip the balance.
Understanding the bounce message
The error message "5.7.1 (undefined status) Message content rejected due to suspected spam. IB703" is a clear indicator. The 5.7.1 status indicates a permanent failure related to security policy rejection. "IB703" is a specific Bigpond internal code for a content-based spam block or blacklist. While the rejection is content-based, it's also worth investigating if the sending IP address or domain has been temporarily or permanently added to a private blocklist (or blacklist) by Bigpond due to previous high spam complaints related to this content.
It's not necessarily a temporary block if it's content-related; it will persist until the offending content patterns are changed or the sender's reputation improves with Bigpond.
Verify your email authentication first
Before diving into content changes, ensure your email authentication records are correctly set up. While a content-based bounce points to the message body, a strong authentication posture builds trust and can sometimes prevent borderline content from being flagged. SPF, DKIM, and DMARC records are fundamental to email deliverability. Bigpond (like most major ISPs) heavily relies on these to verify sender legitimacy.
In fact, Telstra, the parent company of Bigpond, has recently adopted a strict DMARC policy of p=reject for its primary email domains, including bigpond.com. This means that if your emails fail DMARC authentication, they are highly likely to be rejected outright. Proper authentication can impact how content filters weigh your email, potentially giving you more leeway with certain content elements. You can read more about Telstra's DMARC policy changes for further details.
You can also get insights into why your emails are bouncing (or being marked as spam) by consulting resources on general email deliverability issues. These provide a broader perspective on common problems that can lead to rejections, even if the primary cause appears to be content-based. For example, a high rate of user complaints, even if not directly linked to content in the bounce message, can worsen your domain's reputation and make Bigpond's filters more sensitive to your content.
For specific issues, you may want to review why your emails to Bigpond bounce or are marked as spam generally, as content is only one piece of the puzzle. If you recently implemented DMARC changes and are seeing new issues, exploring Bigpond soft bounces related to DMARC is also a good idea, as authentication and content reputation are closely intertwined.
Review and refine your content
Once authentication is confirmed, the next step is a thorough review of your email content. This means looking at every aspect of your email, from the subject line to the unsubscribe link. Here’s a breakdown of common content triggers and how to address them:
Subject line: Avoid excessive capitalization, exclamation marks, special characters, or emojis that could be interpreted as spammy. Certain emojis, especially those associated with urgency or dubious offers, can be problematic.
Body text: Scan for common spam keywords (e.g., "free money," "guaranteed," "urgent"). Reduce the density of such words. Ensure your message sounds natural and human, not like an automated sales pitch.
Links and URLs: Use full, descriptive URLs instead of shortened links. Ensure all linked domains are reputable and not on any public blocklists (or blacklists). Too many links can also be a red flag.
Image-to-text ratio: Emails that are almost entirely images with very little text are often flagged as spam, as they can be used to bypass text-based content filters.
HTML errors and formatting: Poorly coded HTML, hidden text, or unusual fonts and colors can trigger spam filters. Ensure your email renders correctly across various clients.
Consider sending a plain-text version of your email alongside the HTML version. Some spam filters, including those used by Bigpond, may evaluate the plain-text content more heavily or use it as a fallback. Mismatches between HTML and plain text can also be a red flag. Aim for clear, concise, and valuable content that resonates with your recipients. If your emails consistently look like spam to the filters, they will continue to bounce.
Testing your email content before sending can help identify potential issues. While there isn't a definitive Bigpond-specific spam score checker, using general email testing tools can provide insights into how your content is perceived by various spam filters, including common blocklists (or blacklists) that Bigpond might reference. This proactive approach can save you from a lot of bounce issues down the line.
Maintain a strong sender reputation
Maintaining a healthy sender reputation is paramount. Even with perfect content, a poor sender reputation can lead to your emails being flagged. Bigpond considers various factors when assessing your reputation, including your sending volume, bounce rate, complaint rate, and engagement metrics (opens, clicks). A sudden spike in bounces, even content-based ones, can negatively impact this score.
High user complaint rates are a major red flag. If Bigpond recipients are frequently marking your emails as spam, their filters will become more aggressive towards your sender domain and content. This can create a vicious cycle where good emails are also blocked. You can learn more about understanding your domain reputation to proactively monitor this crucial metric.
List hygiene is another critical component. Sending emails to inactive or invalid addresses can increase your bounce rate, signaling to ISPs like Bigpond that you may be engaging in questionable sending practices. Regularly clean your email lists and promptly remove any addresses that result in hard bounces (like the "5.7.1 Message content rejected" error) to ensure your sending reputation remains strong.
Content pitfalls
Spammy keywords: Overuse of words like "free," "guarantee," "win," or illicit terms.
Poor formatting: Excessive capitalization, strange fonts, large images with little text, or broken HTML.
Suspicious links: Shortened URLs, links to unknown or blacklisted domains.
High complaint rates: Recipients marking your emails as spam due to irrelevance or unwanted content.
Content optimization
A/B testing: Test different subject lines and body content variations to see what performs best and triggers fewer filters.
Clear value proposition: Ensure your email's purpose and value are immediately clear and compelling to the recipient.
Personalization: Personalize content where appropriate to increase relevance and engagement.
Engagement tracking: Monitor open rates, click-through rates, and unsubscribe rates. Low engagement can lead to more aggressive filtering.
Steps to resolve and prevent rejections
Resolving content-based spam rejections from Bigpond requires a multi-faceted approach. It's not just about tweaking a few words; it's about understanding and adapting to the nuances of their spam filters and maintaining overall email sending best practices. By systematically reviewing your content, ensuring robust authentication, and prioritizing recipient engagement, you can significantly improve your deliverability to Bigpond and other ISPs.
Always remember that email deliverability is an ongoing process. ISPs continually update their filtering algorithms, and what worked yesterday might not work tomorrow. Consistent monitoring of your email performance and staying informed about industry best practices are key to successful inbox placement. For more general advice on improving email delivery, you might find this article on how to solve email delivery issues helpful.
Views from the trenches
Best practices
Always include a clear and prominent unsubscribe link that is easy to find and use.
Segment your audience and tailor content to ensure relevance, reducing spam complaints.
Monitor your engagement metrics, as low opens or clicks can signal content issues.
Regularly clean your email list to remove inactive or bouncing addresses.
Common pitfalls
Using excessive emojis or special characters in subject lines, especially misleading ones.
Stuffing keywords or using hidden text to try and trick spam filters.
Sending emails with a poor image-to-text ratio, making them look like image-only spam.
Ignoring bounce messages and continuing to send to problematic email addresses.
Expert tips
Test your emails thoroughly using a variety of tools that scan for spam triggers.
Gradually increase sending volume to new domains or segments to build trust.
Engage in two-way communication to foster positive recipient interactions.
Regularly review your DMARC reports for insights into authentication failures and potential content issues.
Expert view
Expert from Email Geeks says a content-based block is likely, and suggested reviewing the mailings that received the block as a warning sign for broader issues.
2023-11-14 - Email Geeks
Marketer view
Marketer from Email Geeks says Bigpond's postmaster is generally helpful with campaign issues or false positives, noting that their thresholds are very tight.
2023-11-15 - Email Geeks
Key takeaways
Experiencing bounce-backs from Bigpond due to content-based spam reasons is a clear signal that your email copy, design, or overall sending practices need adjustment. While the message specifies content, remember that Bigpond's filters are highly sensitive and consider various factors, including your sender reputation and authentication status.
Proactively addressing these issues by reviewing your email content, ensuring proper authentication, and maintaining a clean, engaged email list will not only resolve immediate bounce problems but also fortify your long-term email deliverability with Bigpond and across the board. Staying vigilant about your email practices is key to consistently reaching the inbox.
Bigpond.com addresses can be a frustrating experience. Especially when the bounce reason explicitly states "Message content rejected due to suspected spam," it points directly to an issue within the email's body or subject line. This type of rejection is distinct from authentication failures or recipient address issues. It tells us that Bigpond's (or 
Telstra's) spam filters have identified something within your message itself that triggers their detection algorithms.
