Why did my email open rate suddenly drop and what can I do about it?

Key findings

• Reputation impact: A drop in your domain's reputation, as reported by tools like Google Postmaster Tools, is a strong indicator of deliverability problems leading to lower open rates. This can result in emails being sent to spam or blocked entirely.
• Blocklist issues: If your ESP's sending domain (Return-Path) is on a major blacklist, such as Spamhaus DBL, it can significantly impact inbox placement and artificially lower open rates. Even if it's not your primary sending domain, it can affect email prefetching and filtering. You can check your status using a blocklist checker.
• Authentication and compliance: Failure to comply with major ISP requirements, particularly those from Gmail and Yahoo, regarding email authentication (SPF, DKIM, DMARC) and one-click unsubscribe, can severely impact deliverability and open rates. Check our guide on DMARC, SPF, and DKIM for more.
• Audience engagement: Less engaged audiences, even if recently active, are more prone to lower open rates due to factors like less frequent interaction or higher spam complaint rates.

Key considerations

• ESP competency: If your Email Service Provider (ESP) does not support critical deliverability features like List-Unsubscribe-Post or one-click unsubscribe, it's a significant red flag that their platform may be hindering your deliverability.
• List hygiene and segmentation: Even with regular cleaning, poor segmentation and lax hygiene practices can lead to deliverability issues. Consider more granular segmentation based on recent engagement.
• Machine opens vs. actual opens: Prefetching by ISPs or security software can inflate open rates. A sudden drop might indicate a decrease in actual human engagement or a change in how these machine opens are tracked by your ESP. For more, see how to diagnose an unexpected drop in email engagement.
• Domain reputation and compliance: The combination of a medium domain reputation and non-compliance with major ISP requirements are critical issues that must be addressed first, as they can overshadow other factors.

Key opinions

• Audience segmentation: Segmenting audiences based on recent engagement (e.g., opens in the last month) is a common practice to maintain high engagement, but even this can see drops if underlying issues exist.
• Impact of spam rates: Even a low reported spam rate (e.g., 0.2%) doesn't guarantee inbox placement, as other factors like reputation and blocklists heavily influence filtering.
• GPT limitations: Some marketers rely on internal ESP or Google Postmaster Tools (referred to as GPT) reports, but these might not capture all nuances of deliverability issues, especially those related to ISP-specific filtering or blocklistings.
• ESP control: Many marketers find themselves constrained by their ESP's technical capabilities, particularly concerning compliance with new ISP requirements or unlisting from blacklists, leading to feelings of helplessness.

Key considerations

• Audience quality vs. quantity: While larger, less engaged audiences can provide scale, they also introduce higher risks for deliverability issues compared to highly engaged, smaller segments. This aligns with why a sudden drop in email open rates often points to audience issues.
• Gmail deliverability focus: Given that a large percentage of subscribers are often Gmail users, drops in open rates for this specific ISP are a critical concern and often reflect overall deliverability health.
• Content relevance: Even with engaged lists, if content relevance wanes, subscribers may stop opening. Continuously refining subject lines and content is vital. A sudden drop might indicate low-quality content as a reason.

Key opinions

• ISP compliance: Not meeting Google and Yahoo standards is a critical factor affecting deliverability and, consequently, open rates. This includes proper SPF alignment and support for one-click unsubscribe headers.
• DBL listing impact: A blocklisting (or blacklist) on a major DNSBL like Spamhaus DBL can directly affect email prefetching at Gmail, which then influences reported open rates. Even if it's the ESP's domain that is blocklisted, it still impacts the sender.
• Fundamental issues: Experts stress that if fundamental issues like DBL listings and non-compliance with major ISP requirements are present, other deliverability advice becomes largely irrelevant until these core problems are resolved. This is a common theme when discussing email deliverability issues.
• ESP competency: An ESP that doesn't support essential compliance features is considered incompetent, and staying with such a provider will likely lead to ongoing deliverability challenges.

Key considerations

• Data transparency: Providing all relevant information, such as domain names and audience collection processes, is crucial for accurate diagnosis of deliverability issues. Without it, insights are merely educated guesses.
• List hygiene importance: Poor segmentation and lax list hygiene processes can lead to filters working as intended, meaning emails are blocked due to perceived low quality or spam traps. This is a common cause for sudden email open rate drops.
• ISP prefetching: Prefetching by ISPs (like Gmail) can artificially inflate open rates. If issues like DBL listings or non-compliance affect prefetching, the reported open rates can suddenly drop dramatically, reflecting a more accurate picture of engagement (or lack thereof).
• Platform change: If multiple critical deliverability issues stem directly from the ESP's capabilities and compliance, switching to a more competent platform is often the most effective solution for long-term success, as discussed on Jacob Monash Email Marketing.

Key findings

• Authentication standards: Documentation from major email providers like Google and Yahoo explicitly outlines the necessity of strong email authentication (SPF, DKIM, DMARC) for successful inbox placement. Failure to align with these standards leads to increased filtering.
• One-click unsubscribe: Recent updates from major ISPs emphasize the mandatory implementation of List-Unsubscribe-Post and one-click unsubscribe headers to provide easy opt-out mechanisms, which is crucial for maintaining sender reputation and avoiding spam complaints. Learn more about the Gmail one-click unsubscribe feature.
• Blocklist mechanisms: DNS-based Blocklists (DNSBLs) or Real-time Blackhole Lists (RBLs) aggregate reputation data. A listing on these blocklists, especially for domains involved in the email's authentication chain (like Return-Path), signifies a severe reputation issue that prompts ISPs to reject or spam messages. Read our guide to email blocklists.
• Engagement metrics: While open rates are becoming less reliable due to privacy features, documentation still highlights their importance as an indicator of subscriber interest and deliverability, especially when analyzing trends or comparing engaged vs. less-engaged segments. A drop can suggest blocking or subscriber fatigue, as stated by Salesforce.

Key considerations

• Sender reputation management: Official guidelines underscore that sender reputation is dynamic and influenced by various factors, including spam complaints, bounce rates, and direct unsubscribes. A drop from 'Good' to 'Medium' signals a need for immediate intervention.
• Impact of domain selection: The reputation of all domains involved in the email, including the envelope-from (Return-Path) domain, contributes to overall deliverability. A blocklisted ESP domain can negatively affect the sender's own domain.
• Consistency of standards: Mailbox providers are increasingly aligning their requirements for bulk senders. Non-compliance with one major provider (e.g., Gmail) often means non-compliance with others (e.g., Yahoo, Microsoft), leading to widespread deliverability issues.