What does Mailgun's 'Too old' delivery status message mean and how to troubleshoot it?
Matthew Whittaker
Co-founder & CTO, Suped
Published 26 Jul 2025
Updated 16 Aug 2025
9 min read
Encountering Mailgun's "Too old" delivery status message can be a puzzling experience for email senders. Unlike more descriptive bounce codes, this particular message offers little immediate insight into why your email failed to reach its destination. It leaves many wondering, what exactly does this mean for their email campaigns and, more importantly, how can it be fixed?
This status indicates that Mailgun has ceased attempts to deliver an email because it has remained in its retry queue for an extended period, exceeding the platform's defined maximum retry duration. Essentially, the message expired before successful delivery could occur. It's a permanent failure, meaning Mailgun will no longer try to send that specific email.
While the Too old message itself is generic, the underlying reasons are often related to temporary issues at the recipient's mail server or broader deliverability challenges with your sending domain. Understanding these root causes is crucial for effective troubleshooting and maintaining a healthy email program.
Understanding the 'Too old' error
The Too old status in Mailgun, sometimes associated with internal error codes like 602, signifies that Mailgun's system has given up trying to deliver a particular message. This happens after the platform has made numerous attempts over a specific duration, typically 3 days, but has not received a final acceptance or rejection from the recipient's mail server. Instead, it received temporary failures (soft bounces) or experienced connection issues repeatedly.
Mailgun, like other email service providers, implements a retry mechanism for messages that encounter transient issues. This is a standard practice to ensure delivery even if a recipient's server is temporarily unavailable or overloaded. However, to prevent indefinite queuing and resource drain, there's a hard limit on how long a message will be retried. Once this limit is reached, the message is marked as Too old, indicating a permanent non-delivery.
It is important to note that this is an internal Mailgun disposition response, meaning the error is generated by their platform after numerous delivery attempts. You can find more information about how this message disposition works on Spam Resource.
Common causes leading to the 'Too old' status
The presence of a Too old delivery status can stem from several underlying issues, often related to the recipient's mail server or your sending reputation. Here are the most common culprits:
Recipient server issues: This is a frequent cause. The recipient's mail server might be temporarily down, overloaded, misconfigured, or experiencing network problems, leading to repeated temporary rejections (4xx errors). If these issues persist beyond Mailgun's retry window, the message eventually becomes Too old.
Reputation-based throttling: If your sending IP or domain's reputation is poor, recipient mail servers (especially Microsoft.com and Gmail) might intentionally delay or throttle your emails. This leads to increased temporary rejections and can result in the Too old status. You can learn more about how your domain reputation affects delivery in our guide on high bounce rates and 'too old' bounce responses.
Blocklisting (Blacklisting): If your IP address or domain appears on a public or private blacklist (or blocklist), many mail servers will temporarily reject your emails. Consistent rejections can eventually lead to the Too old status. Find out more about how email blacklists actually work.
Internal Mailgun issues: In rare cases, the issue might be internal to Mailgun's platform, such as running out of connections to a particular provider or an unreported internal failure. This scenario would not show explicit temporary failure codes in your logs prior to the Too old status.
Mailgun's documentation notes that emails are retried until delivery or until a Too old permanent failure is generated, as highlighted in their reporting metrics deep-dive article. This confirms that it's the final status after transient issues.
One common scenario is when emails are sent to Microsoft domains (like Outlook.com, Hotmail.com, Live.com, MSN.com) where Too old bounces are sometimes observed. This indicates that their servers might be actively deferring or queueing messages from specific senders or IPs due to reputation concerns. This isn't unique to Microsoft, as other providers like Gmail and Yahoo (and AOL) also employ similar anti-spam measures.
Troubleshooting steps
Troubleshooting the Too old delivery status requires a systematic approach, as the message itself is a symptom of deeper underlying problems. Here's how to investigate:
Examine Mailgun logs thoroughly: The key to understanding a Too old bounce is to look at the delivery attempts preceding it. Mailgun's logs often show the initial temporary failures or deferrals that ultimately led to the message expiring. Search for the specific message ID or recipient email address and review the entire delivery history for any error codes or messages. These temporary errors often contain more descriptive information, for example, about connection refused or rate limit exceeded messages.
Check recipient domain status: If Too old bounces are concentrated on a specific domain, investigate that domain. Their mail server might be experiencing persistent issues. You can use external tools to check their MX records and server status.
Assess sender reputation: A declining sender reputation is a primary cause of throttling. Check your domain's reputation using tools like Google Postmaster Tools for Gmail recipients. Ensure your SPF, DKIM, and DMARC records are correctly configured and aligned to prevent authentication failures, which negatively impact reputation. Our email deliverability test checklist can help here.
If Mailgun logs provide no preceding temporary error, it's possible the issue is internal to the Mailgun platform. For example, some users on Stack Overflow have reported seeing 602 as an internal error when a message cannot be delivered. In such cases, contacting Mailgun support is the best course of action. They can review internal logs and provide more specific details that are not accessible to users.
Preventing future 'Too old' bounces
Preventing the Too old status requires a proactive approach to email deliverability. Focus on these key areas:
Maintain a clean mailing list: Regularly remove inactive or invalid email addresses. High bounce rates, even soft bounces, can damage your sender reputation over time, leading to throttling and, eventually, Too old messages.
Monitor sender reputation: Stay vigilant about your domain and IP reputation. Tools like Google Postmaster Tools provide valuable insights. If you notice a drop in reputation, address the underlying issues, such as high spam complaint rates or sending to unengaged users.
Implement strong authentication: Ensure your SPF, DKIM, and DMARC records are properly configured. This helps recipient servers trust your emails and reduces the likelihood of throttling. If your DMARC policy isn't enabled, our guide on how to fix policy not enabled warnings can help.
By proactively managing your email list hygiene, monitoring your reputation, and ensuring proper authentication, you can significantly reduce the incidence of Too old bounces and improve your overall email deliverability. This ultimately means more of your important messages reach their intended inboxes.
Views from the trenches
Best practices
Actively monitor your sending reputation with ISPs like Microsoft and Gmail to catch early signs of throttling.
Segment your lists and send to engaged users more frequently to improve engagement metrics and sender reputation.
Implement bounce processing to quickly identify and remove invalid or problematic email addresses.
Use a robust email validation service to clean your lists before sending large campaigns.
Regularly review Mailgun's detailed logs for any temporary failure codes that precede 'Too old' messages.
Common pitfalls
Ignoring early soft bounces, which can accumulate and lead to 'Too old' messages.
Not regularly cleaning your email lists, leading to high bounce rates and poor sender reputation.
Failing to implement proper email authentication (SPF, DKIM, DMARC), which can trigger throttling.
Overlooking specific recipient domains that consistently return 'Too old' errors without deeper investigation.
Relying solely on the generic 'Too old' status without diving into the underlying temporary failure reasons.
Expert tips
Set up alerts for high bounce rates, especially for specific domains, to respond quickly.
Consider a dedicated IP address if you send high volumes and notice shared IP issues.
Engage Mailgun support early if you suspect internal platform issues are contributing to the problem.
Analyze engagement metrics (opens, clicks) to identify disengaged segments that might be generating spam complaints.
Understand the retry policies of your ESP to know how long messages are typically queued before failure.
Marketer view
Marketer from Email Geeks says that they often see 'Too old' messages when there are reputation-based throttling issues with recipient servers like Microsoft domains.
2023-05-09 - Email Geeks
Expert view
Expert from Email Geeks says that 'Too old' is usually a message that occurs after too many delivery attempts, causing the system to stop trying to deliver that message.
2023-05-09 - Email Geeks
Final thoughts on 'Too old' errors
The Mailgun Too old delivery status is a definitive indicator that a message could not be delivered after repeated attempts and has now expired. While the message itself is unspecific, it points to underlying temporary issues with recipient servers or, more commonly, your sending reputation. Addressing these root causes through diligent log analysis, reputation monitoring, and adherence to email best practices is essential. By taking these steps, you can significantly reduce these frustrating bounces and ensure your emails consistently reach their intended recipients.
