Why am I seeing high bounce rates and 'too old' bounce responses, and how is my domain reputation affected?
Michael Ko
Co-founder & CEO, Suped
Published 19 Jul 2025
Updated 19 Aug 2025
8 min read
Seeing a sudden surge in email bounce rates can be alarming. It’s a clear signal that something is amiss with your email program, and it needs immediate attention. Recently, I encountered a situation where a client's newsletter, which included external links to sister brands, saw its bounce rate jump to 14%, particularly with Yahoo and AOL domains. The very next day, a similar campaign, using only internal links, had a significantly lower bounce rate of 2-3%, though still higher than ideal.
This scenario highlights a critical issue: high bounce rates, especially those accompanied by specific responses like 'too old,' are not just delivery failures. They are strong indicators of potential domain reputation damage. Understanding why these bounces occur and how to mitigate their impact is crucial for maintaining healthy email deliverability and ensuring your messages reach the inbox.
Understanding email bounces
Email bounces are broadly categorized into two types: hard bounces and soft bounces. Each signifies a different underlying problem and carries varying implications for your sender reputation.
Hard bounces
A hard bounce indicates a permanent delivery failure. This usually means the email address is invalid, the domain name doesn't exist, or the recipient's server has permanently blocked delivery. Common reasons include misspelled addresses, deleted accounts, or domains that are no longer active. Hard bounces are particularly damaging to your sender reputation because they tell ISPs that you're sending to poor-quality or unverified lists.
Soft bounces
Soft bounces, on the other hand, are temporary delivery failures. These could be due to a full mailbox, the recipient's server being temporarily down, the email message being too large, or a server-side issue. While temporary, repeated soft bounces can still signal problems. Most email service providers (ESPs) will retry sending soft-bounced emails for a certain period before giving up.
The 'too old' bounce phenomenon
The 'too old' bounce response is a specific type of soft bounce, but it indicates a prolonged temporary failure. This message is usually generated by your own Mail Transfer Agent (MTA) or ESP, not directly by the recipient server. It means that the recipient's server (like Mailgun) has been repeatedly (and temporarily) rejecting the message for an extended period, typically three or four days, until your sending server decides the message won't ever be accepted and gives up on it.
In the case of Yahoo and AOL, this 'too old' response often points to a deeper issue related to your sender reputation or the content of your email. These providers are known for their stringent filtering. If they perceive anything suspicious about your sending practices, IP address, or domain, they will often defer messages rather than outright reject them. This deferral can last for days, leading to the 'too old' bounce when your server eventually times out.
One significant factor contributing to this can be the reputation of external links within your email. As observed in the client's case, including links to a sister domain with a lower or compromised reputation can negatively impact the deliverability of your primary domain's emails. This is because ISPs, including Yahoo, scan the entire email, including all linked domains, before deciding to accept or reject a message. If any linked domain has a poor reputation, it can taint the reputation of the entire email and, by extension, your sending domain.
Impact on domain reputation
A high bounce rate, especially a sudden spike or persistent elevation, is a major red flag for Internet Service Providers (ISPs). They interpret it as a sign of poor list quality, outdated data, or even spamming practices. This, in turn, can severely harm your domain reputation and your IP reputation.
Diminished trust: ISPs rely on various signals to determine if an email sender is trustworthy. A consistently high bounce rate suggests you're not maintaining your email lists, which erodes trust and makes ISPs less likely to deliver your emails to the inbox.
Blocklisting (blacklisting): Repeatedly sending to invalid addresses can lead to your IP address or domain being added to a blocklist (or blacklist). This means your emails will be automatically rejected by most receiving servers, regardless of content, severely impacting your deliverability. You can learn more in our guide on email blocklists.
Lower inbox placement: Even if not outright blocked, a damaged reputation means your emails are more likely to land in the spam folder rather than the primary inbox. This reduces your engagement rates and overall campaign effectiveness.
It's important to monitor your bounce rates closely. While an ideal bounce rate is subjective and depends on your industry and list hygiene, many experts recommend keeping it under 2%. A rate above 5% often signals a serious problem that needs immediate attention. Remember, your domain's reputation is built over time, and a sudden drop can be hard to recover from. We explore more about why domain reputation decreases in detail elsewhere.
Strategies to reduce bounce rates and protect your reputation
Addressing high bounce rates and protecting your domain reputation requires a multi-faceted approach, focusing on good email hygiene and authentication.
Regular list hygiene
This is perhaps the most critical step. Regularly clean your email lists by removing invalid or inactive addresses. This includes:
Email validation services: Use third-party tools to verify email addresses before adding them to your list. This helps catch invalid or non-existent addresses. Poor list quality is a leading cause of high bounce rates.
Remove hard bounces immediately: Any address that results in a hard bounce should be removed from your list permanently. Continuing to send to these addresses will only further harm your reputation.
Manage soft bounces: If an email consistently soft bounces over several attempts or campaigns, consider removing it or flagging it for re-engagement. Review our article on soft bounce retry policies.
Robust email authentication
Ensuring your emails are properly authenticated is foundational to good deliverability. Implement and regularly check your SPF, DKIM, and DMARC records. These protocols verify that you are who you say you are, preventing spoofing and improving trust with receiving servers.
Content and link integrity
Be mindful of all links within your email, even those to other reputable domains. If a linked domain has a poor reputation, it can negatively affect yours. Ensure that all links are relevant and point to trustworthy sources. Consider using consistent link tracking domains that align with your sending domain to avoid issues with external domain reputations.
Gradual sending and monitoring
If you're sending to a new or re-engaged list, or have recently faced deliverability issues, consider warming up your IP and domain. This involves gradually increasing your sending volume. Also, continuously monitor your deliverability metrics, including bounce rates, spam complaints, and inbox placement. This allows you to spot issues early and take corrective action.
Views from the trenches
Best practices
Implement a strict email list validation process before sending any campaigns.
Segment your audience and send targeted content to improve engagement and reduce bounces.
Warm up new IPs and domains gradually to build a positive sending history.
Common pitfalls
Not regularly cleaning your email lists, leading to sending to invalid addresses.
Ignoring 'too old' bounce responses, which indicate severe deferral issues.
Using unverified or purchased email lists, resulting in high hard bounce rates.
Expert tips
Use transactional email services for critical communications to ensure higher deliverability.
Regularly review your email content for anything that might trigger spam filters.
Engage with your ESP's deliverability team for advanced diagnostics on 'too old' bounces.
Expert view
Expert from Email Geeks says that 'too old' bounces often indicate that Yahoo (or other ISPs) is temporarily failing the message long enough for the sending server to give up, suggesting a significant reputation challenge.
2024-03-30 - Email Geeks
Marketer view
Marketer from Email Geeks says that sending campaigns with external links to domains with questionable reputations can negatively impact your primary domain's deliverability and increase bounce rates.
2024-04-15 - Email Geeks
Protecting your email sending future
High bounce rates, particularly 'too old' responses from major ISPs, are a critical signal that your email program's health is at risk. They directly impact your domain reputation, leading to lower inbox placement and potential blocklisting (or blacklisting). Ignoring these signals can have long-term negative consequences for your email marketing efforts.
By proactively implementing robust list hygiene, ensuring proper email authentication, being vigilant about all links within your emails, and continuously monitoring your deliverability, you can significantly reduce bounce rates and safeguard your sender reputation. A healthy email program is built on consistent best practices and a keen eye on key performance indicators.
