What's the main difference between a simple 'mailbox full' and a verbose one?

A simple 'mailbox full' is often a temporary issue, while a verbose one, with its extensive technical details like MAPI exceptions, usually indicates a deeper, permanent problem with the mailbox , suggesting it's abandoned or corrupted.

Should I retry sending to an email address that returned a verbose 'mailbox full' bounce?

No, it is highly recommended to not retry sending to addresses that generate these verbose bounces. They are typically hard bounces, and continued attempts can harm your sender reputation and lead to blocklisting (or blacklisting).

How do these verbose bounces affect my email deliverability?

While the initial failure might not directly impact your reputation as much as a spam complaint, consistently sending to addresses that produce these errors suggests poor list hygiene. This can lead to mailbox providers flagging your domain as less reputable, potentially impacting future inbox placement .

What steps should I take to prevent these types of bounces?

Focus on maintaining an engaged and clean email list. Implement double opt-in, regularly remove inactive subscribers, and monitor your bounce rates. If you see a sudden increase in 'mailbox full' deferrals , investigate the cause immediately.

Are these verbose 'mailbox full' bounces common from all mailbox providers?

No, these extremely verbose bounces are primarily characteristic of older or self-hosted Microsoft Exchange environments . Many modern providers, like Gmail and Yahoo , tend to return more concise bounce messages, though some of their mailbox full messages can be excessively long too.

What do extremely verbose 'mailbox full' bounce messages tell us? - Troubleshooting - Email deliverability - Knowledge base

Receiving a bounce message is a routine part of email sending. They inform us when a message couldn't be delivered. While many bounces are straightforward, some are exceptionally verbose, packed with technical jargon and seemingly random alphanumeric strings. These extended "mailbox full" notifications can be intimidating, but they often contain valuable diagnostic information.

When an email returns with a lengthy 554 5.2.2 mailbox full error, it goes beyond a simple "inbox is full" notification. These complex messages usually originate from specific mail systems, most notably

Microsoft Exchange servers, including those used by

Outlook and

Office 365. They provide an internal trace of what went wrong within the recipient's mail system.

Instead of just discarding these verbose bounce messages as noise, understanding them can shed light on underlying issues that affect deliverability. While the sheer volume of data might seem overwhelming, key pieces of information are embedded within, helping to diagnose potential problems on the recipient's end or even reveal deeper patterns in your sending.

Deciphering the verbose bounce message

Let's look at an example of such a verbose bounce message. It typically starts with the standard SMTP error code, followed by a detailed internal exception trace. This trace is essentially a stack dump from the mail server's internal processes.

Example verbose mailbox full bouncesmtp

smtp;554 5.2.2 mailbox full; STOREDRV.Deliver.Exception:QuotaExceededException.MapiExceptionShutoffQuotaExceeded; Failed to process message due to a permanent exception with message Cannot get ID from name. 0.35250:40000830, 1.36674:01000000, 1.61250:00000000, 1.45378:02000000, 1.44866:00000000, 1.36674:02000000, 1.61250:00000000, 1.45378:05000000, 1.44866:14000000, 1.36674:06000000, 1.61250:00000000, 1.45378:12000000, 1.44866:0B000000, 1.36674:A1000000, 1.61250:00000000, 1.45378:21000000, 1.44866:44000000, 1.36674:56000000, 1.61250:00000000, 1.45378:68000000, 1.44866:E80F0000, 16.55847:5F070000, 17.43559:00000000DE030000000000000000000000000000, 20.52176:140FEC88090010106F020000, 20.50032:140FEC887917000012000000, 0.35180:74020000, 255.23226:03009E83, 255.27962:02000000, 255.27962:06000000, 255.17082:DD040000, 0.24929:14004A67, 4.21921:DD040000, 255.27962:FA000000, 255.1494:14004D67, 0.38698:00000000, 7.36354:010000000000010C0B1A239F, 7.36354:010000000000010C1100010 0, 5.29818:0000000030303031366533302D666164612D356331312D303030302D303030303030303030303030002D3932, 1.29920:03000000, 7.29828:5B883EC00300000037393834, 7.29832:000000C003000000F70C2C9B, 4.45884:DD040000, 4.29880:DD040000, 4.59420:DD040000, 7.49544:010000000000010CB9040000, 8.45434:306E0100DAFA115C000000000000000000000000, 5.10786:0000000031352E32302E323238342E3030373A444237505230314D42343535363A33353564356138332D393232312D346237332D616439342D30373831353063373938343800503000000000, 7.51330:592B6D9BBA3DD70805000780, 255.1750:84000000, 255.27962:A1000000, 255.17082:B9040000, 0.27745:89000000, 4.21921:B9040000, 255.27962:56000000, 0.26881:8B000000, 255.21817:B9040000, 0.60978:0A00F636, 0.36402:90000000, 4.38450:DD040000, 0.37224:0A005136, 4.40808:DD040000, 0.24529:0A00F136, 4.18385:DD040000, 0.36864:9A000000, 4.37120:DD040000 [Stage: CreateMessage]

The sheer length of these bounce messages, particularly the hexadecimal codes and MAPI (Messaging Application Programming Interface) exceptions, indicates an issue deep within the recipient's mail infrastructure. It suggests an attempt to deliver the email, which then failed at a low-level storage or processing stage, rather than being rejected outright at the SMTP handshake. This kind of detailed error is primarily for the recipient's mail administrator to debug, but it offers clues to senders too.

Understanding the components

SMTP code: The 554 5.2.2 indicates a permanent failure related to the mailbox, specifically that the mailbox is full. You can learn more about these in what common email bounce messages mean.
STOREDRV.Deliver.Exception: This prefix points to Microsoft Exchange Server's Store Driver component, responsible for delivering messages to mailboxes.
QuotaExceededException: Confirms the core issue, that the recipient has exceeded their storage quota. This is a common cause of full mailbox bounces.
MapiExceptionShutoffQuotaExceeded: A deeper, specific MAPI error indicating the mailbox is full to the point of disallowing further storage.
Hexadecimal Strings: These are internal debugging codes, likely memory addresses or error flags, intended for system administrators.

What these messages truly indicate

While the message clearly states "mailbox full," the verbosity, especially from systems like

Microsoft Exchange, often hints at more than just a recipient who needs to clear their inbox. Such an extensive error might suggest a deeply inactive or neglected account, or even one that has been deliberately abandoned. Modern mailbox providers offer substantial storage, making a truly "full" inbox less common unless it's a very old account or one that is no longer being managed.

These errors are considered permanent failures (hard bounces). A 5xx code like 554 signifies that the email cannot be delivered and retries are unlikely to succeed. This differs from temporary (soft) bounces, which might indicate a transient issue. Therefore, continued attempts to send to such addresses can negatively impact your sender reputation, leading to lower inbox placement rates in the future. You can read more about email bounces and how to handle them.

The "Cannot get ID from name" message, buried within the MAPI exception, is particularly telling. It could suggest an issue with the mailbox's internal structure or a corruption, rather than just a simple quota problem. This is a technical detail that further supports the idea that the account is in a state of disrepair. This is why some senders might observe "mailbox full" bounces followed by subsequent opens, if the recipient clears space, but this is less common with these verbose errors indicating deeper problems.

Traditional 'mailbox full'

Cause: Recipient has exceeded storage limits.
Message: Often concise, like 552 5.2.2 Mailbox full.
Action: Temporary deferral may resolve, or recipient clears space.

Verbose 'mailbox full'

Cause: Exceeded quota, but with underlying system-level issues or potential abandonment.
Message: Extremely detailed, includes MAPI exceptions and internal trace data. Sometimes, Gmail incorrectly marks emails as bounced.
Action: High probability of permanent failure. Suppress immediately.

Actionable steps for senders

When encountering these highly verbose "mailbox full" messages, the best course of action is generally to treat them as hard bounces. Even though the underlying cause is a full mailbox, the complex error typically points to an account that is either neglected or has deeper issues, making successful delivery unlikely in the future.

The primary implication for senders is the need for rigorous list hygiene. Regularly cleaning your email list to remove these types of bouncing addresses is crucial. Continuing to send to addresses that consistently generate permanent bounce errors can damage your sender reputation and increase your spam rate with mailbox providers. This can lead to your emails being filtered into spam folders, or even your domain being added to a blocklist (or blacklist).

Monitoring your bounce rates diligently, especially for these specific error types, is a key part of maintaining good deliverability. Tools like

Google Postmaster Tools can provide insights into your bounce rates and domain reputation. For more advanced monitoring, services that offer detailed bounce analytics can help you identify trends and problematic recipients. You can also troubleshoot email bounce messages more broadly.

Best practices for handling verbose bounces

Immediate suppression: Add the recipient's email address to your suppression list immediately after receiving this type of hard bounce.
List hygiene: Regularly clean your email lists to remove inactive or bouncing addresses. This prevents repeat issues and protects your email domain reputation.
Monitor bounce rates: Keep a close eye on your overall bounce rates. A sudden increase, particularly from specific domains, could indicate a larger issue or a sudden spike in Gmail 'mailbox full' deferrals.
Segmentation: Consider segmenting your lists based on engagement to proactively identify and prune less active contacts before they generate bounces.

The role of mailbox providers

The highly detailed nature of these bounce messages, often seen from systems like

Microsoft Exchange, highlights a specific philosophy of error reporting. While many providers opt for more concise bounce codes to prevent information leakage or simply because it's sufficient for most senders, others provide an internal diagnostic trace. This verbose output is primarily for the recipient's IT team or mail administrator to troubleshoot internal server issues, rather than for external senders to fully decode.

It's a balance: providing too little information can make debugging difficult for the recipient's admin, while too much can be overwhelming and, as observed, seemingly unnecessary for the external sender. However, this level of detail confirms that the message successfully reached the recipient's mail server and was then rejected by their internal mail store, rather than being blocked earlier in the SMTP conversation due to reputation issues or policy violations.

For senders, this implies that the problem lies specifically with the recipient's mailbox state. It's not necessarily a sign that your emails are being perceived as spam or that your sending practices are problematic, but rather that the particular destination mailbox is inoperable for the moment, perhaps permanently.

Views from the trenches

Best practices

Implement automated bounce processing to instantly suppress hard bounce addresses, including verbose mailbox full errors.

Monitor bounce codes and their associated text for patterns, especially for unexpected spikes or unusual messages.

Regularly audit your email list for inactive subscribers and consider re-engagement campaigns or removal if they're not responsive.

Ensure your email authentication (SPF, DKIM, DMARC) is correctly configured to build and maintain strong sender reputation.

Common pitfalls

Ignoring verbose bounce messages or treating all 'mailbox full' errors as temporary, leading to continued sending to invalid addresses.

Not segmenting lists, which can result in sending to disengaged users who are more likely to generate hard bounces.

Failing to monitor mailbox provider specific bounce patterns, which can reveal underlying deliverability issues.

Overlooking the context of the bounce message, which might differentiate a temporary issue from a permanent one.

Expert tips

Always focus on maintaining a clean and engaged subscriber list to minimize all types of bounces, including complex ones.

Use DMARC reports to gain deeper insights into how mailbox providers are processing your emails and identify authentication failures.

Be proactive with re-engagement campaigns to identify truly active subscribers versus abandoned accounts.

Understand that a 'mailbox full' error can also signal a low-activity spam trap, warranting immediate suppression.

Marketer view

Marketer from Email Geeks says they often see these overly detailed bounce messages and find most of the information unnecessary for everyday use.

September 20, 2019 - Email Geeks

Marketer view

Marketer from Email Geeks says they appreciate that the actual problem is usually stated early in the bounce message, even if a lot of extra data follows.

September 20, 2019 - Email Geeks

Conclusion

Extremely verbose "mailbox full" bounce messages, particularly those originating from

Microsoft Exchange environments, are more than just simple indicators of a full inbox. They are complex diagnostic reports, primarily intended for the recipient's technical team, but they offer valuable cues for senders. The presence of MAPI exceptions and extensive internal trace data often points to a permanent issue with the recipient's mailbox, suggesting it might be abandoned or corrupted, rather than just temporarily over quota.

For email marketers and senders, the key takeaway is to treat these verbose messages as hard bounces. Promptly suppressing these addresses from your lists is vital for maintaining a healthy sender reputation and ensuring long-term email deliverability. While these messages can seem like an "overachiever" in error reporting, their underlying message is clear: stop sending to this address.