Why are my emails soft bouncing with Bigpond after implementing DMARC changes?
Matthew Whittaker
Co-founder & CTO, Suped
Published 13 Jul 2025
Updated 17 Aug 2025
7 min read
Dealing with email soft bounces can be incredibly frustrating, especially after you've put in the effort to implement DMARC. When those bounces specifically target Bigpond.com email addresses and present an error message like '558 5.7.1 Message content rejected due to suspected spam. IB703', it can feel like you're hitting a wall.
Many senders, particularly those using marketing platforms like Klaviyo, encounter this issue. It's a clear sign that while your DMARC setup might be technically correct, Bigpond's filters are flagging your content or sender reputation as problematic. This is often an issue distinct from your authentication passing or failing.
The key here is that a soft bounce is a temporary rejection. While frustrating, it indicates that the receiving server is not outright refusing the email due to a hard authentication failure, but rather due to a policy-based or content-based issue. This leaves room for troubleshooting and improvement.
Bigpond, being a significant ISP in Australia, is known for its stringent email filtering. Recently, Telstra (Bigpond's parent company) implemented a p=reject DMARC policy for its primary domains, including bigpond.com. This means they are more aggressive in rejecting emails that don't pass DMARC alignment, but also those that trigger their internal spam filters.
The error message, 'Message content rejected due to suspected spam', points directly away from DMARC, SPF, or DKIM authentication issues, and towards the actual content of your email or your sender reputation. While DMARC is vital for authentication, it doesn't directly filter content. Instead, it instructs the receiving server on how to handle emails that fail authentication. If your emails are passing authentication but still bouncing, it's a strong indicator that other factors are at play.
Understanding this distinction is crucial. You might have a perfectly configured DMARC record, but if your email content or overall sending practices appear suspicious to Bigpond's systems, they will still soft bounce your messages. This is why a 95.5% bounce rate, even with good DMARC, is alarming and points to deeper issues.
Bigpond's strict filtering
Telstra Bigpond employs advanced spam detection. Even if your email passes DMARC, SPF, and DKIM, the content itself can trigger rejections if it resembles spam, contains suspicious links, or exhibits characteristics of bulk unsolicited mail. Their p=reject policy also means they're not afraid to bounce emails that don't meet their stringent standards.
Revisiting your DMARC, SPF, and DKIM setup
When you implement DMARC, you're setting a policy for how receiving mail servers should handle emails that claim to be from your domain. This involves SPF (Sender Policy Framework) and DKIM (DomainKeys Identified Mail). SPF checks if the sending IP is authorized, while DKIM verifies that the email hasn't been tampered with in transit. Both need to align with your DMARC policy for an email to pass DMARC.
However, even with a robust DMARC policy in place, if your DMARC reports show pass for Bigpond but you're still seeing soft bounces, the problem isn't the authentication itself, but what happens after successful authentication. It suggests other factors are influencing deliverability.
For a comprehensive understanding, ensure your DMARC, SPF, and DKIM records are correctly configured and aligned. If you suspect an alignment issue, even if DMARC reports show passes, it's worth reviewing. For example, some ESPs might send from different subdomains that require specific DKIM configurations. This is a common reason why emails go to spam due to authentication failures, but your specific error points to content, not authentication.
The phrase 'Message content rejected due to suspected spam' is a direct signal that Bigpond's spam filters are reacting to something within your email. This can be anything from specific keywords, excessive use of capitalization or exclamation marks, too many images relative to text, or suspicious links.
Sender reputation plays a huge role here. Even if your domain is authenticated, if your sending IP or domain has a poor reputation with Bigpond (or any ISP for that matter), your emails are more likely to be scrutinized and rejected. A sudden increase in volume to previously unengaged subscribers, or sending to stale lists, can rapidly tank your sender reputation. This often leads to Bigpond emails bouncing with content-based reasons.
A 95.5% bounce rate, even soft bounces, indicates a significant issue that needs immediate attention. It suggests that a large portion of your emails are not reaching the inbox due to content or reputation triggers. This can severely impact your campaign performance and overall domain standing, similar to how emails might land in spam during domain warm-up if content or volume isn't managed properly. You need to identify what specific elements in your email are triggering the spam filters.
Content vs. authentication
If DMARC reports show your emails are passing authentication, the problem isn't usually with your SPF or DKIM alignment. Instead, Bigpond's content filters or your sender reputation are likely flagging your messages as spam. This can happen if your email volume suddenly increases, if you send to unengaged users, or if your content contains problematic elements. The IB703 code confirms a content-based rejection, meaning the message itself is deemed suspicious.
Steps to improve Bigpond deliverability
To address these soft bounces, especially with Bigpond, you need to shift your focus from authentication to content and list hygiene. First, rigorously clean your email list. Sending to unengaged or invalid email addresses is a primary driver of poor sender reputation and high bounce rates.
Next, critically evaluate your email content. Remove any potentially spammy phrases, reduce image-to-text ratios, and ensure all links are clean and relevant. Try sending a plain-text version of your email to a small segment of Bigpond addresses to see if it passes. This can help isolate whether the issue is structural or content-related. Remember that fixing soft bounces often involves these steps.
Finally, consistent monitoring of your email deliverability is key. Use DMARC reports to ensure authentication is always passing, and regularly run email deliverability tests to major ISPs, especially sensitive ones like Bigpond. This proactive approach helps you catch issues before they escalate into widespread deliverability problems.
Issue
Solution
Spammy keywords/phrases
Review email copy for promotional language, excessive exclamation marks, or trigger words. Focus on clear, concise messaging.
High image-to-text ratio
Ensure your emails have sufficient text content relative to images. Spam filters often flag image-heavy emails.
Suspicious links
Check all links for redirects, shortened URLs, or domains with poor reputations. Use clear, direct links.
Poor sender reputation
Focus on list hygiene, segmenting engaged users, and gradually increasing volume. Address any blacklist or blocklist issues promptly.
Views from the trenches
Best practices
Regularly audit your email list for engagement, removing inactive subscribers to maintain a healthy sending reputation.
Segment your audience aggressively, sending your most valuable content to highly engaged subscribers.
A/B test different email content elements, including subject lines and body copy, to identify what performs best.
Monitor your DMARC reports daily to quickly identify any authentication issues, even if they aren't the primary cause of soft bounces.
Common pitfalls
Assuming DMARC implementation solves all deliverability problems, overlooking content-based rejections.
Sending high volumes to unengaged or old email addresses, especially after DMARC changes, which can quickly harm reputation.
Using generic email templates or content that is common with spammers, triggering ISP filters.
Ignoring bounce messages and error codes, which provide critical clues about the underlying problem.
Expert tips
When encountering 'content rejected' errors, simplify your email design and text. Start with plain text and gradually add elements to pinpoint the trigger.
Bigpond is highly sensitive. Consider a separate sending strategy or IP for them if they continue to be a problem, although this is a last resort.
Verify that your sending platform is correctly handling unsubscribe requests, as high complaint rates will contribute to poor reputation.
Collaborate with your ESP's deliverability team to analyze bounce logs and identify specific patterns or content that triggers rejections.
Expert view
Expert from Email Geeks says that Bigpond is extremely sensitive to sending volume and engagement, so high volumes to less engaged segments can quickly lead to soft bounces even with DMARC in place.
2024-02-15 - Email Geeks
Marketer view
Marketer from Email Geeks says that they tightened their engaged segment to 14 days, but still saw a 95.5% bounce rate, highlighting that engagement alone might not be enough if other factors are at play.
2024-02-15 - Email Geeks
Navigating Bigpond deliverability challenges
Soft bounces from Bigpond after DMARC changes, especially with a content-rejected message, underscore a critical aspect of email deliverability: authentication is necessary, but not always sufficient. While DMARC strengthens your domain's credibility, the content of your emails and your overall sender reputation remain paramount, particularly with ISPs known for strict filtering.
Addressing these issues requires a holistic approach: meticulous list hygiene, content optimization, and continuous monitoring. By focusing on these areas, you can significantly improve your chances of reaching the inbox, even with challenging recipients like Bigpond users.
Bigpond.com email addresses and present an error message like '558 5.7.1 Message content rejected due to suspected spam. IB703', it can feel like you're hitting a wall.
Klaviyo, encounter this issue. It's a clear sign that while your DMARC setup might be technically correct, Bigpond's filters are flagging your content or sender reputation as problematic. This is often an issue distinct from your authentication passing or failing.
Telstra Bigpond employs advanced spam detection. Even if your email passes DMARC, SPF, and DKIM, the content itself can trigger rejections if it resembles spam, contains suspicious links, or exhibits characteristics of bulk unsolicited mail. Their p=reject policy also means they're not afraid to bounce emails that don't meet their stringent standards.
