Why does Return Path report rejections when my ESP doesn't show high bounce rates?

Return Path's data is aggregated from a specific network of ISPs and spam traps, which is a subset of the entire email ecosystem. Your ESP reports on all your sending attempts and their outcomes. Discrepancies often arise because Return Path's observations are based on their monitoring network's experience, which may not perfectly reflect your overall deliverability across all providers.

What kind of "sender rejection" does Return Path typically identify?

Return Path's "sender rejection" typically means that mail from your IP or domain was refused by an ISP within their monitoring network. This often happens if your sending reputation is low or you are listed on an email blocklist (or blacklist). It signifies a block at the connection level before the email even enters the recipient's system.

How can I get more detailed rejection data from my ESP?

You can get more detailed rejection data from your ESP by requesting specific bounce logs, which include SMTP error codes, and reviewing your complaint reports. Many ESPs provide dashboards with these metrics, but deeper analysis might require requesting raw logs or consulting with their deliverability support team. This helps identify the exact reasons for rejections.

Should I be concerned if Return Path flags an issue, but my ESP says everything is fine?

Yes, you should investigate any issues flagged by Return Path, even if your ESP's data looks fine. Return Path's data can act as an early warning system, indicating potential problems with specific ISPs or general reputation before they impact your broader sending. Compare the data to see if a small but significant segment of your audience is affected.

What are the main causes of email rejections from an ISP's perspective?

From an ISP's perspective, common causes of email rejections include sending to invalid or non-existent addresses (leading to hard bounces), hitting spam traps, high complaint rates, being listed on a blocklist (or blacklist), poor sender reputation, or failing email authentication checks like SPF, DKIM, and DMARC. Content filters can also trigger rejections if the email appears to be spam.

How should I interpret sender rejection data from ReturnPath compared to my ESP? - Sender reputation - Email deliverability - Knowledge base

It can be confusing when an email service provider's (ESP) data on sender rejections doesn't match what you see from reputation monitoring services like Return Path. These discrepancies are common, and understanding them is crucial for effective email deliverability.

While your ESP provides direct insights into bounces and complaints from mail servers, Return Path offers a broader, network-based view of how your mail is perceived, often focusing on aggregate reputation scores and blocklist (or blacklist) listings. I'll help you interpret these different datasets and figure out what action you should take.

The nature of sender rejection data

When Return Path reports "sender rejection," it typically indicates that their monitoring network observed mail from your IP address or domain being refused at the point of connection by various mail servers. This often happens if your sending IP or domain is listed on a blocklist or has a low sender reputation. I often check if being on a blocklist is the issue, as this can severely impact your deliverability, as seen in Spamhaus's description of Return-Path.

Your ESP, on the other hand, reports on bounces, which are a more granular form of rejection. A "hard bounce" means permanent failure, while a "soft bounce" implies a temporary issue. ESPs also track spam complaints. The key difference is that Return Path observes rejections in their network, while your ESP reports on rejections specific to your actual sends.

It's important to remember that Return Path's data comes from a subset of internet service providers (ISPs), particularly those in the United States. This can mean their observed rejection rates might not perfectly mirror your overall deliverability across all recipients, leading to differing metrics compared to your ESP.

Understanding Return Path data sources

Return Path (now Validity) aggregates data from a specific network of ISPs and spam traps. While valuable, this network doesn't represent the entire internet's mail flow. Their reported sender rejection rates reflect what they observe within their particular data streams, which may be skewed.

Deciphering the different perspectives

Your ESP's bounce logs provide specific error codes and reasons for rejections, which are critical for diagnosing issues. This real-time, detailed feedback is often the most accurate reflection of your immediate sending performance. This is why it's vital to know how to get SMTP bounce logs.

Return Path's view

Sender Score: A reputation algorithm from HubSpot, based on complaints, spam traps, and volume, is a general indicator, but does not guarantee deliverability.
RBL rejections: Their network observes if your IPs are listed on blocklists, leading to outright rejections from participating mail servers.

ESP's view

Bounce rates: Detailed reports on hard (permanent) and soft (temporary) bounces with specific SMTP error codes.
Complaint rates: Direct feedback from recipients marking your emails as spam, often routed through feedback loops.
Actual delivery: Reflects the outcomes of every email you attempt to send, providing the most accurate picture of your direct deliverability.

Return Path's Sender Score, while a useful indicator of your IP's reputation, doesn't always translate directly to inbox placement. Factors like subscriber engagement carry significant weight with mailbox providers. I've found that sometimes, a high Sender Score on its own doesn't translate to higher inbox placement rates, as subscriber engagement is a major factor, as Mailjet noted in their blog. The apparent discrepancy often stems from these different data sources. Your ESP sees every mail you attempt to send and every response. Return Path observes how your mail is treated by a specific network of ISPs and spam traps.

Practical steps to investigate rejections

The first step is to consult your ESP's detailed bounce and complaint reports. Look for patterns in the rejection codes. Are specific domains or ISPs rejecting your mail more frequently? Understanding these specific error messages will provide a clearer picture of the underlying problem.

Pay close attention to any sudden spikes in bounces or complaints that align with Return Path's rejection alerts. If your ESP's data corroborates a rise in rejections, then you likely have an issue that needs immediate attention, such as poor list hygiene or unexpected blocklist (or blacklist) placement. I often cross-reference this with other tools like Google Postmaster Tools to get a more complete picture.

Example SMTP rejection messagetext

550 5.7.1 Service unavailable; client host [192.0.2.1] blocked using zen.spamhaus.org; See http://www.spamhaus.org/query/ip/192.0.2.1

A common reason for rejections is sending to unengaged or invalid addresses, which can trigger spam traps. Even if your list is opt-in, regular cleaning is essential. For instance, sometimes email addresses on your list end up on a blocklist. This can lead to your emails going to spam or being rejected.

Proactively check blocklists

If you are seeing significant "sender rejection" from Return Path (or any similar service), it's advisable to proactively check if your sending IPs or domains are listed on any major public blocklists (or blacklists). Being listed means mail servers might refuse your emails outright. This can be critical for your email domain reputation.

Cultivating long-term deliverability

Proactive monitoring is key. Don't rely on just one source for your deliverability metrics. Combine the detailed reporting from your ESP with insights from reputation services like Return Path and Google Postmaster Tools for a comprehensive overview. This holistic approach provides the best understanding of your sender reputation and deliverability issues.

Maintain impeccable list hygiene. Regularly remove unengaged subscribers and bounced addresses. Implementing double opt-in for new subscribers significantly reduces the risk of collecting invalid or problematic email addresses. This proactive cleaning helps in improving your sender score and overall inbox placement.

Metric	Reported by ESP	Reported by Return Path
Bounce Codes	Yes, with specific SMTP errors	Less granular, aggregate rejection rates
Complaint Rates	Yes, from FBLs and direct reports	Contributes to Sender Score, but not raw rate
Inbox Placement Rate	Inferred from delivery data, limited visibility	Via seeds and panel data, can be more comprehensive
Sender Reputation Score	Internal ESP scores, not public	Public Sender Score

Strong email authentication is non-negotiable. Ensure your SPF, DKIM, and DMARC records are correctly configured and aligned. Proper authentication helps mailbox providers verify your identity and reduces the likelihood of rejections based on spoofing or phishing concerns. If persistent "sender rejection" issues arise, especially with major providers, open a dialogue with your ESP's support team. They have deeper insights into their infrastructure and can help diagnose complex deliverability challenges.

Views from the trenches

Best practices

Compare Return Path data directly with your ESP's bounce logs to identify specific rejection types and volumes.

Prioritize investigating rejections from ISPs where you have a large percentage of your subscriber base.

Regularly clean your email lists to remove unengaged subscribers and invalid addresses, reducing spam trap hits.

Common pitfalls

Panicking over Return Path's aggregate rejection numbers without cross-referencing with your ESP's detailed data.

Ignoring specific SMTP error codes from your ESP, which pinpoint the exact reasons for rejections.

Assuming a good Sender Score from Return Path guarantees optimal inbox placement, neglecting engagement metrics.

Expert tips

Engage with your ESP's support team for insights into transient or deferred errors not immediately visible in basic reports.

Utilize other reputation tools like Google Postmaster Tools for a diversified view of your email performance.

Proactively monitor public blacklists (or blocklists) for your sending IPs and domains, as these directly cause rejections.

Marketer view

Marketer from Email Geeks says that if bounce rates from your ESP aren't matching Return Path's rejection rates, it might be due to Return Path's data sources being heavily weighted towards specific US ISPs, so it's not always a cause for alarm.

2020-02-25 - Email Geeks

Expert view

Expert from Email Geeks says that if you're a Return Path customer, you should contact their support to understand the specifics of the rejection data, including the volume and period, before taking drastic action.

2020-02-25 - Email Geeks

Key takeaways

Interpreting sender rejection data requires a nuanced approach. While Return Path provides valuable reputation insights from its network, your ESP offers the direct, granular details of your email deliveries. By cross-referencing both datasets, focusing on specific error codes, maintaining excellent list hygiene, and ensuring proper authentication, you can gain a complete understanding of your email performance and address any deliverability challenges effectively. A balanced view, considering both the macro and micro data, is always the most effective strategy for ensuring your emails reach the inbox.