What causes high bounce rates during IP warming, and how can they be fixed?

Summary

High bounce rates during IP warming are a multifaceted issue primarily driven by data quality, sender reputation, and user trust. Invalid or outdated email addresses, poor data validation processes, and a lack of proper bounce handling contribute significantly. Sending to nonexistent addresses, failing to gain user trust in providing valid email addresses, and inadequate list hygiene practices exacerbate the problem. To mitigate these issues, it's crucial to clean email lists regularly, implement double opt-in processes, use real-time email verification, segment lists effectively, warm up sending volume gradually, ensure proper email authentication (SPF, DKIM, DMARC), and monitor seed lists to identify deliverability issues early on. Low engagement rates can also indirectly increase bounces, highlighting the importance of relevant content and targeted audience engagement.

Key findings

  • Data Quality Issues: Invalid and outdated email addresses are leading causes of high bounce rates during IP warming.
  • Lack of Trust and Value: Users may provide fake addresses due to a lack of trust or perceived value, contributing to higher bounce rates.
  • Poor Bounce Handling: Failure to properly handle bounces, including incorrect segmentation and bounce processing, worsens deliverability issues.
  • Sender Reputation: High bounce rates negatively impact sender reputation, potentially leading to increased spam filtering or blocking.
  • Insufficient Warm-up: Rapid IP warming can trigger spam filters, increasing bounce rates and damaging sender reputation.
  • Inadequate Authentication: Lack of proper email authentication (SPF, DKIM, DMARC) increases the likelihood of emails being marked as spam and bouncing.

Key considerations

  • Implement Validation Processes: Employ real-time email verification services on signup forms to prevent invalid addresses from entering the list.
  • Clean and Segment Lists: Regularly clean email lists to remove invalid, unengaged, or inactive subscribers. Segment lists effectively to ensure relevant content is delivered.
  • Warm Up Gradually: Incrementally increase sending volume during IP warming to avoid triggering spam filters and damaging sender reputation.
  • Ensure Proper Authentication: Verify that SPF, DKIM, and DMARC are correctly configured to authenticate emails and improve deliverability.
  • Monitor Seed Lists: Utilize seed lists to monitor deliverability during IP warming and identify issues early on.
  • Prioritize Engagement: Focus on creating valuable content and targeting the right audience to improve engagement and reduce the likelihood of being flagged as spam.

What email marketers say
11Marketer opinions

High bounce rates during IP warming are primarily caused by issues related to data quality, sending practices, and authentication. Key factors include sending to invalid or outdated email addresses, poor data validation processes, rapid warming schedules, lack of proper email authentication, and low engagement. Solutions involve cleaning email lists, implementing double opt-in, using email verification services, segmenting lists effectively, warming up sending volume gradually, and ensuring proper authentication (SPF, DKIM, DMARC).

Key opinions

  • Data Validation: Invalid or outdated email addresses are a primary cause of high bounce rates. Poor data validation processes contribute to this issue.
  • List Hygiene: Outdated or purchased email lists, along with poor data hygiene (unengaged subscribers), significantly impact bounce rates.
  • Warming Speed: Warming up sending volume too quickly can trigger spam filters and result in increased bounce rates.
  • Authentication: Lack of proper email authentication (SPF, DKIM, DMARC) increases the likelihood of emails being marked as spam and bouncing.
  • Engagement: Low engagement rates (opens, clicks) can indirectly increase bounces as ISPs may identify unengaged subscribers as potential spam traps.
  • Segmentation: Improper list segmentation, resulting in irrelevant content being sent to subscribers, contributes to higher bounce rates.

Key considerations

  • Data Quality: Regularly clean email lists to remove invalid or inactive addresses. Implement email validation tools and processes.
  • Opt-in Process: Use double opt-in to ensure subscribers have actively verified their email address. This reduces typos and invalid addresses.
  • Gradual Warm-up: Gradually increase sending volume during IP warming to avoid triggering spam filters and high bounce rates.
  • Authentication Setup: Ensure proper email authentication (SPF, DKIM, DMARC) is correctly configured before and during IP warming.
  • Content Relevance: Segment lists effectively to ensure emails are targeted and relevant, improving engagement and reducing bounces.
  • Engagement Monitoring: Monitor engagement rates and focus on creating valuable content to target the right audience, minimizing the risk of being flagged as spam.
Marketer view

Marketer from Email Geeks suggests to investigate where the invalid addresses originate from, and to focus on plugging that source, guessing that the web channel may be a good starting point.

April 2023 - Email Geeks
Marketer view

Email marketer from MailerLite states that improper email list segmentation can lead to high bounce rates if irrelevant content is sent to subscribers. Refining your segments ensures that emails are targeted, reducing bounces and improving engagement.

December 2024 - MailerLite
Marketer view

Email marketer from Reddit user r/marketing suggests that implementing a confirmed opt-in process ensures that subscribers have actively verified their email address. This eliminates typos and invalid addresses, drastically reducing bounce rates during IP warming.

September 2021 - Reddit
Marketer view

Marketer from Email Geeks suggests that invalid addresses at scale indicate poor data validation, which can make the sender appear as a spammer to message filters.

August 2022 - Email Geeks
Marketer view

Email marketer from Email on Acid shares that without proper email authentication (SPF, DKIM, DMARC), your emails are more likely to be marked as spam, leading to bounces. Ensure your authentication is correctly configured before and during IP warming.

January 2023 - Email on Acid
Marketer view

Email marketer from Gmass states that low engagement rates (opens, clicks) can indirectly increase bounces as ISPs see unengaged subscribers as potential spam traps. Focus on creating valuable content and targeting the right audience during IP warming.

August 2023 - Gmass
Marketer view

Email marketer from Neil Patel explains that high bounce rates during IP warming can be caused by sending to old or invalid email addresses. He recommends using email validation tools to clean your list and improve deliverability.

October 2021 - Neil Patel
Marketer view

Email marketer from HubSpot shares that a key cause of high bounce rates is outdated or purchased email lists. They advise using double opt-in and regularly scrubbing your list to remove inactive subscribers, therefore fixing the bounce rates.

May 2021 - HubSpot
Marketer view

Email marketer from Litmus explains that poor data hygiene, like sending to old or unengaged subscribers, results in high bounce rates. Regular data cleansing and re-engagement campaigns are vital during IP warming to maintain a healthy list.

January 2025 - Litmus
Marketer view

Email marketer from Marketing Over Coffee Forum states the bounce rate will be affected if you warm up too quickly. Its essential to start with a small volume and gradually increase it to avoid triggering spam filters and high bounce rates.

April 2021 - Marketing Over Coffee Forum
Marketer view

Email marketer from Reddit user r/emailmarketing explains that using a real-time email verification service on signup forms can prevent invalid addresses from entering your list in the first place. This proactive approach minimizes bounce rates during IP warming.

May 2024 - Reddit

What the experts say
5Expert opinions

High bounce rates during IP warming often stem from inadequate data handling and list hygiene. Addressing issues such as unhandled bounces, sending to nonexistent addresses, and failing to gain user trust in providing valid email addresses are essential. Regular list cleaning to remove invalid or unengaged addresses, along with the use of seed lists for monitoring deliverability during IP warming, are crucial steps in improving sender reputation and reducing bounce rates.

Key opinions

  • Bounce Handling: Data not being properly bounce handled indicates a need for improved segmentation and bounce processing.
  • Reputation Impact: Sending repeated messages to nonexistent addresses can harm sender reputation, leading to deliverability issues.
  • User Trust: High bounce rates can result from users providing fake addresses due to a lack of trust or perceived value. Addressing these concerns can improve data accuracy.
  • List Hygiene: Poor list hygiene, including invalid or unengaged addresses, is a major cause of high bounce rates during IP warming.
  • Seed List Monitoring: Using seed lists to monitor deliverability during IP warming helps identify issues early, allowing for prompt corrective actions.

Key considerations

  • Data Segmentation: Ensure data is properly segmented and that bounce handling processes are in place to manage invalid addresses.
  • Address Verification: Implement strategies to verify email addresses at signup, such as offering a 'skip' option while still encouraging valid entries.
  • List Cleaning: Regularly clean email lists to remove invalid or unengaged addresses, improving overall list hygiene.
  • Trust Building: Focus on building trust and demonstrating value to encourage users to provide accurate email addresses.
  • Deliverability Monitoring: Use seed lists and monitor deliverability metrics during IP warming to identify and address issues promptly.
Expert view

Expert from Word to the Wise explains that high bounce rates during IP warming can indicate issues with list hygiene. Focus on removing invalid addresses and those who haven't engaged recently to improve your sender reputation.

December 2023 - Word to the Wise
Expert view

Expert from Word to the Wise shares using a seed list during IP warming, and monitoring where those test emails land (inbox, spam, blocked) is crucial. A high bounce rate within the seed list indicates serious deliverability issues that need immediate attention.

January 2022 - Word to the Wise
Expert view

Expert from Email Geeks suggests that a high bounce rate means email address requirements are putting people off giving real addresses due to a lack of trust or perceived value. He recommends offering a "skip" option and checking submitted addresses in realtime.

September 2021 - Email Geeks
Expert view

Expert from Email Geeks warns that sending repeated messages to nonexistent addresses can harm your reputation.

January 2025 - Email Geeks
Expert view

Expert from Email Geeks explains that the data hasn't been bounce handled. She recommends to inform whoever did the segmentation that they need to fix it.

January 2023 - Email Geeks

What the documentation says
3Technical articles

High bounce rates during IP warming are significantly influenced by the quality of email lists and sending practices. Hard bounces, caused by invalid email addresses, and soft bounces, resulting from temporary issues, both require monitoring to identify and address data quality and infrastructure problems. Maintaining a low bounce rate is critical for preserving sender reputation, achieved by regularly cleaning email lists and gradually increasing sending volume during the IP warming process.

Key findings

  • Bounce Types: Hard bounces (invalid addresses) and soft bounces (temporary issues) provide insights into data quality and infrastructure.
  • Reputation Impact: High bounce rates negatively affect sender reputation, making deliverability a challenge.
  • List Hygiene: Cleaning email lists of invalid or inactive addresses is vital for reducing bounce rates.
  • Warming Process: Gradually increasing sending volume during IP warming helps maintain a low bounce rate.

Key considerations

  • Monitoring Bounces: Regularly monitor both hard and soft bounces to diagnose data quality and infrastructure issues.
  • Data Quality: Ensure the email list is clean and contains valid, active addresses to minimize hard bounces.
  • Warming Strategy: Incrementally increase sending volume to avoid overwhelming email providers and maintain a positive sender reputation.
  • Ongoing Maintenance: Continuously clean and update email lists to remove invalid or inactive addresses and manage sender reputation.
Technical article

Documentation from SendGrid emphasizes that a high bounce rate negatively impacts sender reputation. During IP warming, it's crucial to maintain a low bounce rate by ensuring a clean email list and gradually increasing sending volume.

March 2023 - SendGrid
Technical article

Documentation from SparkPost advises regularly cleaning email lists to remove invalid or inactive addresses, which reduces bounce rates. This is critical during IP warming to establish a positive sending reputation.

October 2024 - SparkPost
Technical article

Documentation from Mailjet explains that hard bounces occur due to invalid or non-existent email addresses, while soft bounces are temporary issues like a full inbox or server problems. Monitoring both during IP warming helps identify data quality and infrastructure issues.

September 2023 - Mailjet