How should email marketers handle permanent bounce errors like full or inactive mailboxes?
Matthew Whittaker
Co-founder & CTO, Suped
Published 1 Jun 2025
Updated 17 Aug 2025
7 min read
Email marketers often face the challenge of bounce errors, which can significantly impact deliverability and sender reputation. Among these, permanent bounce errors, such as those indicating a full mailbox or an inactive account, require particular attention. Unlike soft bounces, which are temporary issues, permanent bounces signal that an email will never be delivered to that specific address. Ignoring these signals can lead to severe consequences for your email program.
Understanding the nuances of these permanent failures is crucial for maintaining a healthy email list and ensuring your messages reach their intended recipients. When an email server consistently rejects your mail with a permanent error, it’s a clear indication that the address is no longer viable. Continuing to send to such addresses can flag your domain as a sender of undesirable mail, potentially leading to blocklisting (or blacklisting) and diminished inbox placement rates across all your campaigns.
Understanding permanent bounce types
Permanent bounces are typically identified by 5.x.x SMTP error codes, indicating a permanent failure. This differs from temporary (or soft) bounces, which are often indicated by 4.x.x codes and suggest issues like a temporary server outage or a full mailbox that might clear up. However, sometimes a mailbox full error can also be a permanent bounce.
For instance, an 552 5.2.2 Mailbox full error can indicate a permanent situation if the mailbox has been abandoned and is no longer being checked or cleared. Providers like Gmail specifically might return messages like “The recipient’s inbox is out of storage space and inactive,” suggesting a permanent issue tied to account inactivity. This is a strong signal that the account is effectively dead, not just temporarily full.
It’s important to distinguish between these scenarios. A truly temporary mailbox full error might resolve itself if the recipient clears space. However, if the error message also indicates inactivity, or if you consistently receive a 5.x.x code for a full mailbox, it's best to treat it as a permanent bounce. This proactive approach safeguards your sender reputation and ensures your email list remains clean and effective.
Repeatedly sending emails to invalid or inactive addresses that result in permanent bounces can severely damage your sender reputation. Internet Service Providers (ISPs) and email services like Google and Yahoo monitor bounce rates as a key indicator of sender quality. A high hard bounce rate suggests poor list hygiene, which can lead to your emails being directed to the spam folder, or worse, your sending IP or domain being added to a blocklist (or blacklist).
When your domain or IP address ends up on a major blocklist, it can prevent your emails from reaching a wide range of recipients, impacting your entire email marketing strategy. This is why immediate action on permanent bounces is not just a best practice, but a necessity for long-term deliverability. You should be proactive about understanding what happens when your domain is blocklisted.
Beyond deliverability, a high bounce rate can skew your engagement metrics, making it harder to accurately assess campaign performance. Sending to disengaged or non-existent email addresses inflates your send volume without yielding results, wasting resources and masking the true engagement levels of your active subscribers. Regularly cleaning your list is fundamental for improving deliverability by sunsetting inactive subscribers.
Strategies for managing permanent bounces
The primary strategy for handling permanent bounce errors is immediate suppression. Once an email address hard bounces, it should be removed from your active mailing lists and added to a suppression list. This prevents future attempts to send to that address, protecting your sender reputation. Most Email Service Providers (ESPs) automatically handle hard bounces by suppressing these addresses.
For "mailbox full" errors, especially if they are 4.x.x soft bounces, some retry logic can be applied. However, if these soft bounces persist over multiple sends, or if the bounce message explicitly states inactivity or permanent rejection, they should be treated like hard bounces and suppressed. This is critical for determining which bounce types to eliminate versus monitor.
Email verification services are invaluable tools for preventing permanent bounces before they occur. Running your email lists through a verifier can identify invalid or non-existent addresses, and even potential spam traps, allowing you to clean your list proactively. This pre-send verification is a cornerstone of effective email bounce reduction and list hygiene.
Another strategy is to implement a re-engagement process for contacts showing signs of life outside email. If a user with a bouncing email address logs into your website or uses your app, it might be worth a targeted re-engagement attempt, perhaps through a different channel, before fully suppressing their email address. This selective approach balances deliverability with customer retention.
Immediate suppression
Hard bounces: Automatically remove these email addresses from your active mailing lists. They represent permanent failures.
Inactivity signals: If a mailbox full error comes with an explicit message about account inactivity, treat it as a hard bounce.
Implementing a bounce management workflow
A robust bounce management workflow is essential. Your ESP should provide detailed bounce reports that categorize errors by type. Utilize this data to automatically suppress hard bounces. For persistent soft bounces (e.g., repeated mailbox full errors), consider implementing a threshold, such as three consecutive soft bounces, before classifying them as permanent and suppressing them. This helps improving list hygiene by suppressing soft bounces.
Regular list cleaning goes beyond automated suppression. Periodically review your entire email list for inactive subscribers, even those not generating bounce errors. Segmenting your audience based on engagement and gradually sunsetting disengaged contacts can significantly improve your overall deliverability and reduce the likelihood of hitting inactive accounts or spam traps. This proactive approach supports managing hard and soft bounces in your campaigns.
It’s also important to stay informed about major ISP policy changes. Providers like Microsoft, Apple, Google, and Yahoo frequently update their deliverability requirements, often with a focus on sender authenticity and list hygiene. Proactive adjustments to your sending practices based on these updates can prevent unforeseen spikes in bounce rates or blocklisting events.
By actively monitoring your bounce reports and implementing a robust list management strategy, you can maintain a strong sender reputation and achieve higher inbox placement rates. This is a continuous process that requires vigilance and adaptation to the evolving email ecosystem.
Views from the trenches
Best practices
Actively monitor your bounce reports and classify bounces as permanent (hard) or temporary (soft).
Immediately suppress all email addresses that generate hard bounces to protect your sender reputation.
Implement a consistent policy for persistent soft bounces, converting them to hard bounces after a set number of retries or time.
Use email validation services to clean your lists before sending large campaigns, reducing upfront bounce rates.
Common pitfalls
Ignoring permanent bounce errors, leading to repeated attempts to send to dead addresses.
Failing to differentiate between temporary and permanent mailbox full errors, and retrying indefinitely.
Not having an automated system for suppressing hard bounces, causing manual overhead and reputation damage.
Neglecting to clean your email list regularly, resulting in a higher likelihood of hitting spam traps.
Expert tips
For accounts showing permanent mailbox full errors, especially those indicating inactivity, do not send mail until there is a clear sign of engagement elsewhere.
Consider a re-engagement campaign for users with persistent soft bounces, focusing on actions beyond just email opens, like website logins or purchases.
If an email address is bouncing, consider showing an alert on your website to the user, informing them you cannot send emails to their registered address.
Understand that different Mailbox Providers (MBPs) have varying sensitivities to sending to dead addresses; tailor your strategy accordingly.
Expert view
Expert from Email Geeks says Gmail has two versions of mailbox full bounces, a 4.x.x for temporary and a 5.x.x for permanent and disabled mailboxes, with data calculated across all Google products like photos and drive.
Feb 22, 2024 - Email Geeks
Expert view
Expert from Email Geeks says the changes from Yahoo and Google will be gradual over the next couple of months, so not seeing anything yet does not mean issues won't arise in the future.
Feb 22, 2024 - Email Geeks
Maintaining a healthy email ecosystem
Effectively managing permanent bounce errors is a cornerstone of successful email marketing. By promptly identifying and suppressing problematic addresses, leveraging email verification tools, and implementing intelligent re-engagement strategies, marketers can protect their sender reputation and improve overall deliverability. This diligent approach ensures that your marketing efforts are focused on engaged subscribers, leading to better campaign performance and a healthier email ecosystem.
Remember, email deliverability is an ongoing process that requires constant attention and adaptation. By staying proactive and informed, you can minimize bounce rates and maximize your inbox placement.
Gmail specifically might return messages like “The recipient’s inbox is out of storage space and inactive,” suggesting a permanent issue tied to account inactivity. This is a strong signal that the account is effectively dead, not just temporarily full.
Google and 
Yahoo monitor bounce rates as a key indicator of sender quality. A high hard bounce rate suggests poor list hygiene, which can lead to your emails being directed to the spam folder, or worse, your sending IP or domain being added to a blocklist (or blacklist).
Microsoft, 
Apple, Google, and Yahoo frequently update their deliverability requirements, often with a focus on sender authenticity and list hygiene. Proactive adjustments to your sending practices based on these updates can prevent unforeseen spikes in bounce rates or blocklisting events.
