Summary
High bounce rates, particularly 'too old' messages from Verizon/AOL, stem from a combination of factors, including list quality issues (invalid addresses, outdated lists), aggressive greylisting/rate limiting, poor sender reputation, high complaint rates, and evolving email provider policies. 'Too old' messages usually indicate the ESP has tried delivering the email for several days without success. Hard bounces are permanent failures; soft bounces are temporary. Resolutions involve email authentication (SPF, DKIM, DMARC), thorough list cleaning and validation, implementing double opt-in, carefully managing sender reputation, and contacting the ESP for shared IP problems, with the addition of throttling when receiving 421 errors from Verizon/AOL.
Key findings
- List Quality is Key: Invalid addresses, outdated lists, and lack of engagement are primary contributors to high bounce rates.
- Authentication is Mandatory: SPF, DKIM, and DMARC are increasingly necessary to prove sender credibility to mailbox providers like Yahoo, AOL, and Gmail, reducing the chance of being flagged as spam.
- Sender Reputation Matters: A good sender reputation, cultivated through opt-in practices, relevant content, and consistent list hygiene, significantly impacts deliverability.
- Verizon/AOL specifics: “Too old” bounces are common with Verizon and AOL due to aggressive Greylisting, Rate Limiting and High complaint rates.
- Types of Bounces: Bounces are defined as either hard (permanent) or soft (temporary).
Key considerations
- Validate Email Addresses: Implement email validation services to remove invalid and risky addresses before sending campaigns.
- Practice List Hygiene: Remove inactive subscribers, implement sunset policies, and regularly clean the email list.
- Use Double Opt-In: Require new subscribers to confirm their subscription to prevent invalid emails and improve list quality.
- Throttle and Retry: For AOL/Verizon issues with 421 errors, consider throttling your email flow and retrying later to mitigate bounce issues.
- Monitor Bounce and Complaint Rates: Keep a close watch on bounce and complaint metrics, establishing feedback loops to address deliverability problems immediately.
- ESP Communication: Communicate with the ESP on shared ip issues to see if problems are widespead.
What email marketers say
8 marketer opinions
High bounce rates, particularly with Verizon (Yahoo, AOL), can be caused by several factors, including issues with email lists (invalid addresses, outdated or purchased lists), deliverability problems, greylisting/rate limiting, poor sender reputation, and changes in email provider policies. Solutions involve list cleaning, double opt-in, email authentication (SPF, DKIM, DMARC), monitoring sender reputation, contacting the ESP for shared IP issues, and validating email addresses before sending.
Key opinions
- List Hygiene: Maintaining a clean email list by removing invalid, unengaged, and outdated addresses is crucial to reduce bounce rates.
- Email Authentication: Implementing SPF, DKIM, and DMARC is essential to verify email sender identity and improve deliverability, especially with stricter guidelines from Yahoo, AOL, and Gmail.
- Sender Reputation: A positive sender reputation is vital; it can be improved by optimizing opt-in processes, ensuring content relevance, and practicing good list hygiene.
- Double Opt-In: Using double opt-in ensures that subscribers have explicitly confirmed their interest in receiving emails, which leads to a more engaged audience and reduces bounces.
- ESP Contact: When using a shared IP and encountering high bounce rates, contacting the email service provider (ESP) is important to investigate whether the issue is widespread or specific to the account.
- Verizon Specific Issues: If 'too old' bounces are primarily from AOL/Verizon, the issue might stem from aggressive greylisting/rate limiting. Throttling email flow and retrying later, along with monitoring complaint rates, can help.
- Email Validation: Validating email addresses with a validation service before sending any emails to remove any non-existent emails which reduces bounce rate.
Key considerations
- List Segmentation: Segmenting your email list and tailoring content to specific audience segments can increase engagement and reduce bounce rates.
- Monitoring Bounce Rates: Regularly monitoring bounce rates and taking prompt action to address any spikes or unusual activity is essential for maintaining email health.
- Content Relevance: Ensure your email content is relevant and valuable to your subscribers to minimize complaints and maintain a positive sender reputation.
- ESP Communication: Maintain open communication with your ESP to stay informed about any policy changes or issues that may impact email deliverability.
- Gradual Warm-up: When sending to an old list, use an email verification service for the first send. Remove non-existent emails to help reduce the chances of being blocked by any mail servers.
- Greylisting: Greylisting or rate limiting is a method of defense against email spam, where a mail server makes a temporary refusal.
Marketer view
Email marketer from ActiveCampaign answers that to improve and maintain email list health, focusing on list hygiene is vital, which consists of removing inactive or unengaged subscribers from your email list. In addition, they share that you can focus on your sender reputation as this ensures that your email provider knows that you are credible.
20 May 2025 - ActiveCampaign
Marketer view
Email marketer from MailerLite shares that reducing your bounce rate involves validating email addresses before sending. They suggest using email validation services, cleaning your list of unengaged subscribers, and only sending to subscribers who have explicitly opted in to receive your emails. Segmenting your lists and personalizing emails can also help improve engagement and reduce bounces.
29 Dec 2023 - MailerLite
What the experts say
3 expert opinions
The 'too old' bounce message from Verizon/AOL usually indicates that the ESP repeatedly tried to deliver the email over several days without success, often due to aggressive greylisting and rate limiting, especially for senders with lower reputations. Microsoft/Verizon is declining the emails. High complaint rates contribute significantly. Solutions include throttling email flow, re-evaluating opt-in processes, and warming up the email process. In addition, authenticating emails with SPF, DKIM and DMARC helps with proving sender credibility.
Key opinions
- Aggressive Greylisting/Rate Limiting: AOL/Verizon employs aggressive greylisting and rate limiting, especially for senders with less stellar reputations, leading to 'too old' bounces.
- High Complaint Rates: High complaint rates can trigger 'too old' bounces. Managing sender reputation is key.
- Email Authentication: Authenticating emails with SPF, DKIM, and DMARC is increasingly important due to new requirements by AOL and Yahoo.
- Delivery Attempts: 'Too old' messages generally mean the ESP has retried delivery for 3-4 days without success.
Key considerations
- Permission Collection: Re-evaluate permission collection methods and recipient expectations to ensure they align and minimize complaints.
- Email Warm-up: After pausing sending, warm up the email process to rebuild sender reputation gradually.
- Opt-in Process Optimization: Optimize opt-in processes to improve sender reputation and reduce the likelihood of being classified as a poor sender.
- Throttling: Throttling email flow and retrying delivery later can mitigate 'too old' bounces due to resource issues (421 errors).
- Sender Reputation Management: Actively managing sender reputation by optimizing opt-in processes, content relevance, and list hygiene helps avoid being classified as a poor sender.
Expert view
Expert from Word to the Wise, Laura Atkins, explains that AOL/Verizon’s “too old” bounces are often due to aggressive greylisting and rate limiting, especially for senders with a less-than-stellar reputation. She advises that if bounces are related to '421' or 'resource unavailable', the solution may be to throttle the email flow and retry later. She also explains, high complaint rates are often a root cause, so managing sender reputation by optimizing opt-in processes, content relevance, and list hygiene can help to avoid or mitigate being classified as a poor sender.
29 Jan 2023 - Word to the Wise
Expert view
Expert from Spamresource explains that AOL and Yahoo Mail are implementing new email authentication requirements for senders. As of now, they recommend that all senders authenticate their email with SPF, DKIM, and DMARC, and to make it easier for users to unsubscribe.
31 Dec 2024 - Spamresource
What the documentation says
3 technical articles
Bounce messages are categorized as either hard (permanent failures like invalid email addresses) or soft (temporary issues like server unavailability). Monitoring bounce and complaint rates is crucial for maintaining a good sender reputation, and actions should be taken if rates exceed acceptable thresholds. SMTP Enhanced Mail System Status Codes provide a standardized way to communicate bounce reasons, including both permanent and transient errors.
Key findings
- Hard vs Soft Bounces: Bounces are classified as hard (permanent failure) or soft (temporary issue).
- Sender Reputation: Maintaining a good sender reputation depends on monitoring and addressing bounce and complaint rates.
- SMTP Status Codes: SMTP Enhanced Mail System Status Codes offer a standardized method to communicate bounce reasons.
Key considerations
- Rate Monitoring: Regularly monitor both bounce and complaint rates to identify potential deliverability issues.
- Feedback Loops: Implement feedback loops to process bounce notifications and automatically remove invalid addresses from sending lists.
- Actionable Thresholds: Define acceptable thresholds for bounce and complaint rates, and take immediate action when these thresholds are exceeded.
- Bounce Management: Managing bounce rates and addressing their root causes is important for deliverability.
Technical article
Documentation from SparkPost explains that bounces are classified into hard and soft bounces. Hard bounces indicate permanent delivery failures (invalid email), while soft bounces are temporary issues (server unavailable). They emphasize that managing bounce rates and addressing the causes are important for deliverability.
28 Jul 2021 - SparkPost
Technical article
Documentation from RFC describes SMTP Enhanced Mail System Status Codes. These codes are returned by mail systems to indicate the outcome of a mail delivery attempt. They provide a standardized way to communicate the reason for bounces, including permanent and transient errors.
27 Dec 2024 - RFC
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