Summary
A drop in email open rates between subject line tests and full sends, especially in Gmail, can be attributed to several factors. Firstly, Gmail's method of automatically downloading images complicates open rate measurement. Secondly, the shift to the Promotions tab versus the Primary inbox can cause open rate decreases. Also, there are several factors around content/sending habits and reputation management to be aware of. These are; (1) variations in authentication, content, list quality, and sending habits between A/B tests and the full send can negatively affect sender reputation; (2) Gmail's algorithm learns from the initial test send and adjusts its filtering; (3) changes in the audience, their engagement, and fatigue with the subject lines between tests and full sends all contribute to open rate fluctuations. To mitigate this, marketers should prioritize consistent practices, maintain good sender reputation through IP warming and email verification, properly segment and clean their lists, and adhere to SMTP standards.
Key findings
- Gmail Image Downloads: Gmail's automatic image downloading affects open rate metrics, making it harder to determine true inbox placement.
- Promotions Tab: Emails landing in the Promotions tab instead of the Primary inbox can cause a noticeable drop in open rates.
- Sender Reputation: Changes in sender reputation, content, and sending habits between tests and full sends can negatively impact deliverability.
- Gmail Learning: Gmail's algorithm learns from the initial test send and may adjust filtering for the full send based on user engagement.
- List & Audience Changes: Differences in audience, list segmentation, user engagement, and subject line fatigue between tests and full sends can affect open rates.
Key considerations
- Monitor Image Prefetching: Consider that Gmail's image prefetching influences open rate data; use other metrics to assess deliverability.
- Seed list testing and Email Placement Monitoring: Monitor inbox placement across different tabs to gauge deliverability.
- Maintain Consistent Practices: Ensure consistent email authentication, list quality, and sending habits between test and full sends.
- Optimize Content & Sending: Prioritize user engagement by sending relevant, valuable content and optimize the sending schedule and frequency.
- Manage Sender Reputation: Warm up sending IPs, verify email lists, and adhere to SMTP standards to maintain a positive sender reputation.
- Sampling Size: Make sure that the size of your sampling list for any A/B tests, is representative of your full sending list.
What email marketers say
13 marketer opinions
Email open rates can drop between subject line tests and full sends, particularly in Gmail, due to several factors. These include differences in audience, list segmentation, and timing between the test and the full send. Gmail's learning algorithms adjust filtering based on initial engagement, and negative engagement during the test can negatively impact the full send. List fatigue, where recipients become desensitized to subject lines, also plays a role. Technical aspects, such as sender reputation (impacted by IP warming and email verification), authentication (SPF, DKIM, DMARC), and email list hygiene (removing invalid addresses), are crucial for maintaining good deliverability. Consistent practices across tests and full sends, along with seed list monitoring, help ensure stable inbox placement.
Key opinions
- Gmail Filtering: Gmail learns from user engagement with test sends and adjusts filtering accordingly, so negative engagement in tests can impact the full send.
- Audience Differences: The audience responding to a test subject line differs from those of the full send, so A/B testing must be performed in a sample representative of the full sending list.
- List Fatigue: Recipients exposed to test subject lines may be less likely to open the full send, particularly if the subject lines are similar, leading to subject line fatigue.
- Sender Reputation: IP warming and email verification practices affects Sender reputation.
- Technical Factors: Email authentication (SPF, DKIM, DMARC) and list hygiene impact email placement.
Key considerations
- List Segmentation: Segment lists appropriately to minimize list fatigue.
- Test Sample: A/B test your sample with a segment that is representative of your full sending list to minimize testing bias.
- Engagement Monitoring: Continuously check email placements as these may change throughout campaigns and over time as your business changes.
- Deliverability: Maintain a good sender reputation through IP warming and verifying email addresses.
- Authentication Protocols: Authenticate emails using SPF, DKIM, and DMARC to improve deliverability.
Marketer view
Email marketer from HubSpot Blog shares it's important to ensure that A/B testing is conducted with a representative sample of your audience, otherwise the results can mislead your full send and lead to a drop in open rates.
8 Sep 2023 - HubSpot Blog
Marketer view
Email marketer from Campaign Monitor Blog notes that the initial exposure to the test subject line may reduce the effectiveness of the winning subject line in the full send, particularly if the audience remembers seeing it recently. This 'list fatigue' can decrease open rates.
20 Dec 2024 - Campaign Monitor Blog
What the experts say
4 expert opinions
Email open rates can drop between subject line tests and full sends, particularly in Gmail, due to several factors related to Gmail's specific handling of emails and the overall quality and consistency of email practices. Gmail's automatic image downloading complicates open rate measurement and shifts in sending habits, content, and list quality between tests and full sends can harm sender reputation, further impacting inbox placement. A common reason is the move to the Promotions tab instead of the Primary inbox. Consistent email authentication, list quality, and sender behavior are crucial for maintaining deliverability.
Key opinions
- Gmail's Image Prefetching: Gmail automatically downloads images, including tracking pixels, which complicates accurately measuring if an email lands in the inbox vs. spam based solely on open rates.
- Promotions Tab Placement: Emails may land in the Promotions tab rather than the primary inbox, which can lead to a noticeable decrease in open rates (around 20% is common).
- Sender Reputation Sensitivity: Gmail's algorithms are sensitive to sudden changes in sending habits, content, and authentication between A/B tests and the full send, affecting sender reputation and deliverability.
- Inconsistent Practices: Variations in email authentication, content, and list quality between test sends and the full send impact deliverability, as ISPs like Gmail use these signals to determine inbox placement.
Key considerations
- Account for Image Prefetching: Understand that Gmail's image prefetching affects open rate metrics. Consider other metrics to gauge deliverability and engagement.
- Monitor Inbox Placement: Keep an eye on inbox placement (Primary vs. Promotions tab) in Gmail to understand changes in deliverability.
- Maintain Consistent Practices: Ensure consistent email authentication (SPF, DKIM, DMARC), list quality, and sender behavior across all sends (including tests) to maintain a positive sender reputation.
- Avoid Sudden Shifts: Avoid sudden changes in sending habits, content, and list quality to prevent negative impacts on sender reputation, especially when sending to Gmail.
Expert view
Expert from Email Geeks shares that because google automatically downloads all images, including pixels when someone logs into gmail, a single point in time measurement of ‘opens’ doesn’t really tell us anything about whether or not the mail is going to spam.
4 Mar 2022 - Email Geeks
Expert view
Expert from Email Geeks suggests that the mail could be going to the promotions tab instead of the inbox tab, which can cause a 20% drop in open rates.
1 Aug 2022 - Email Geeks
What the documentation says
4 technical articles
Documentation from various sources indicates that a drop in email open rates between subject line tests and full sends, particularly in Gmail, is attributable to several factors. Sender reputation is crucial, with changes between tests and full sends affecting deliverability. Gmail's complex spam filtering algorithm considers sender reputation, email content, and user engagement. Seed list testing helps monitor inbox placement. Adhering to SMTP standards ensures reliable delivery. Changes to content or practice between A/B tests will cause a drop off in results, and therefore must be consistent.
Key findings
- Gmail's Spam Filter: Gmail utilizes a complex algorithm to filter spam based on sender reputation, content, and engagement, impacting inbox placement.
- Sender Reputation Impact: Sender reputation is a key factor influencing email deliverability and open rates; changes between test and full sends can negatively affect it.
- Seed List Testing: Seed list testing offers insights into inbox placement by comparing test and full sends, helping identify deliverability issues.
- SMTP Standards: Adherence to SMTP standards is essential for reliable email delivery; deviations can lead to deliverability problems.
Key considerations
- Monitor Sender Reputation: Consistently monitor and maintain a positive sender reputation to improve email deliverability.
- Test with Seed Lists: Utilize seed list testing to compare inbox placement and identify potential deliverability issues between test and full sends.
- Adhere to SMTP Standards: Ensure compliance with SMTP standards to enhance email deliverability.
- Email Content & Engagement: Ensure consistency in email content and user engagement and content, and do not change between A/B test and full send.
Technical article
Documentation from Google Support explains that Gmail uses a complex algorithm to filter spam, taking into account factors such as sender reputation, email content, and user engagement. Changes in any of these factors between the test and full send can affect placement.
26 Oct 2022 - Google Support
Technical article
Documentation from SparkPost explains that seed list testing can provide insights into inbox placement. By comparing the placement of test and full sends using seed lists, you can identify potential deliverability issues.
16 Feb 2024 - SparkPost Documentation
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