What is an SMTP 552 error and how should it be managed?
Matthew Whittaker
Co-founder & CTO, Suped
Published 10 Jul 2025
Updated 18 Aug 2025
7 min read
An SMTP 552 error indicates that an email message could not be delivered to its recipient. This is typically a permanent failure, meaning the email server is definitively refusing to accept the message.
When you encounter a 552 error, it means the recipient's mail server has rejected your email. This usually happens for two primary reasons: the recipient's mailbox is full, or the message size (including attachments) exceeds the server's limits. Managing these errors is crucial for maintaining good email deliverability and ensuring your messages reach their intended inboxes.
Understanding the SMTP 552 error
The 552 SMTP status code is a class 5xx permanent negative completion reply, which signifies that the server encountered a fatal error and cannot complete the request. While classified as permanent, some systems may initially treat certain 552 variations as temporary, particularly those related to transient overload. However, for most practical purposes, it signals a non-deliverable message.
The most common causes behind a 552 error relate to the recipient's mailbox conditions or the message content itself. A recipient's mailbox might be over quota, meaning it has reached its storage limit and cannot accept new emails. Alternatively, the message you are sending, particularly if it includes large attachments, might exceed the maximum size allowed by the receiving server. This can also include instances where specific file types are not permitted.
Beyond size and quota, a 552 error can occasionally indicate that the email was rejected due to content policies or spam filtering. For example, some mail servers may incorrectly return a 552 error when a URL within the message is found on a domain blocklist or a blacklist. This specific behavior has been observed with certain ISPs, where a 552 error might be returned instead of a more specific spam rejection code, as highlighted in discussions around Gmail's 552 5.7.0 errors.
Error Code / Message
Meaning
Typical Cause
552 5.2.2 user is overquota
Recipient's mailbox is full
Recipient has exceeded their storage limit
552 5.3.4 message size exceeds fixed maximum message size
Email is too large for the recipient's server
Message, especially attachments, is larger than the allowed limit
552 5.2.0 sender rejected AUP#POL
Email rejected by policy (Acceptable Use Policy)
Content, sender, or attachments violate the recipient's mail policy, sometimes related to spam
Diagnosing and identifying 552 errors
Identifying a 552 error begins with reviewing your bounce messages or email logs. When an email bounces, the sending server typically receives a Non-Delivery Report (NDR) or bounce message that includes the SMTP error code and a more descriptive explanation. These messages are critical for understanding why your email was not delivered.
Look for specific phrases within the bounce message that elaborate on the 552 code. Common messages include Requested mail action aborted: exceeded storage allocation, user is overquota, or message size exceeds fixed maximum message size. These provide direct clues as to whether the issue is related to the recipient's storage capacity or the size of your email.
Example 552 bounce message for mailbox fullplain
From: Mail Delivery Subsystem <mailer-daemon@example.com>
To: your_email@yourdomain.com
Subject: Undelivered Mail Returned to Sender
This message was created automatically by mail delivery software.
A message that you sent could not be delivered to one or more of its recipients.
This is a permanent error. The following address(es) failed:
recipient@example.com:
SMTP error from remote mail server after end of data: 552 5.2.2 The email account that you tried to reach is over quota.
It's important to differentiate between a 552 error caused by a full mailbox and one caused by message size. While both result in non-delivery, the required resolution strategies differ. Checking the specific bounce message is paramount. For instance, an error like 552 5.2.0 sender rejected AUP#POL points to a policy-based rejection, which requires a different approach than a simple size or quota issue. You can learn more about specific policy rejections, such as Xfinity's 552 5.2.0 rejection policy.
Strategies for managing and preventing 552 errors
Managing 552 errors effectively requires a two-pronged approach: immediate mitigation and long-term prevention. For mailbox full errors, consider if the recipient needs to clear their inbox. For message size limits, you may need to reduce attachment sizes or send large files via cloud storage links instead of direct attachments. This is a common solution, as detailed by Mailpro on fixing 552 errors.
In some cases, especially with smaller or less robust ISPs, a 552 error related to a full mailbox might be transient due to server overload rather than a permanently full inbox. For such scenarios, suspending sending for a short period (e.g., 24-48 hours) and then gradually re-engaging with a segmented, highly engaged audience from that specific ISP can help resolve the issue. This strategy focuses on slowly rebuilding trust and capacity with the receiving server.
Audience segmentation: Focus on sending to engaged recipients to reduce bounce rates and improve sender reputation.
List hygiene: Regularly clean your email lists to remove inactive or bouncing addresses. This prevents repeated attempts to problematic mailboxes, which can hurt your deliverability. Consider how SuprSend advises on list maintenance.
Content optimization: Keep email sizes manageable. If large attachments are necessary, use cloud sharing or links.
Immediate actions for message size errors
Reduce attachment size: Compress files or remove unnecessary elements.
Use cloud storage: Share links to large files via services like Google Drive or Dropbox.
Immediate actions for mailbox full errors
Inform recipients: Advise them to clear their mailbox. You might try sending a plain text email later.
Temporary suspension: Pause sending to the problematic recipient for 24-48 hours.
Long-term prevention for all 552 errors
Maintain list hygiene: Regularly remove inactive or bouncing addresses to ensure high quality email deliverability.
Segment audiences: Send targeted emails to highly engaged segments, especially for smaller ISPs.
Monitor volume: Gradually increase sending volume to new or problematic domains to avoid overwhelming servers.
Implementing a robust blocklist monitoring strategy is also beneficial. While a 552 error doesn't directly mean you're on a blacklist (blocklist), a pattern of high bounce rates, even due to recipient-side issues, can negatively impact your sender reputation over time and potentially lead to future blocklistings. Proactive monitoring helps you quickly detect and address issues before they escalate.
Impact on deliverability and sender reputation
Even though a 552 error primarily signals an issue on the recipient's side, repeated occurrences can still damage your sender reputation. ISPs and email providers track bounce rates, and a consistently high rate of 552 errors, whether due to full mailboxes or excessive message sizes, can signal that your sending practices are inefficient or that your list quality is poor.
Providers like Yahoo and AOL might start throttling your emails or routing them to the spam folder if they detect a pattern of rejected messages. This happens because high bounce rates can be indicative of outdated lists or, in some cases, even spamming behavior, leading to a decline in your domain reputation.
Reputation risk overview
Increased bounce rates: ISPs see numerous 552 errors as a negative signal, impacting how they view your sending behavior.
Throttling and deferrals: Your emails might be intentionally slowed down or temporarily rejected.
Spam folder placement: A degraded reputation can lead to more emails landing in spam folders for other recipients.
Promptly addressing 552 errors and actively managing your email lists are crucial steps in maintaining a healthy sender reputation. Ignoring these bounces can lead to broader deliverability issues, affecting all your email campaigns, not just those to problematic recipients. Ensuring your email practices align with best standards will help you avoid being categorized as a risky sender and prevent your emails from ending up on a blacklist or blocklist.
Views from the trenches
Best practices
Actively monitor your bounce logs for 552 errors, categorizing them by cause (size vs. quota) for better action.
Segment your audience, especially for smaller ISPs, to send to highly engaged recipients first.
Implement a regular list cleaning process to remove invalid or persistently bouncing addresses.
Optimize email content and attachment sizes to stay within common server limits.
Common pitfalls
Ignoring 552 errors, which can lead to negative sender reputation and broader deliverability issues.
Continuously attempting to send large emails to recipients with size limits or full mailboxes.
Failing to segment your list and sending high volumes to smaller, less robust ISPs, overwhelming their systems.
Not distinguishing between different 552 sub-codes, leading to ineffective troubleshooting.
Expert tips
For small ISPs that occasionally return 552 errors due to high traffic, pause sending for 24-48 hours and then re-engage slowly.
Even if an ISP incorrectly categorizes a valid address as a hard bounce with a 552, your platform might still mark it as invalid if it doesn't match specific soft bounce keywords, so watch your categorization rules.
Always check the specific bounce message details as the 552 code can be used for various rejections, including content filtering or even blacklisting.
A spike in 552 errors, especially from a particular domain, may indicate that the recipient server is experiencing resource limitations, rather than an issue with your email content.
Marketer view
Marketer from Email Geeks says they started seeing a sudden increase in 552 errors from charter.net contacts, which typically showed very low bounce rates.
2019-03-22 - Email Geeks
Expert view
Expert from Email Geeks says that the 552 error series can be either a soft or hard bounce, depending on keywords in the bounce message. Bounce categorization rules are designed to be conservative to avoid marking deliverable addresses as hard bounces.
2019-03-24 - Email Geeks
Key takeaways for email senders
The SMTP 552 error is a significant bounce code that indicates a permanent delivery failure, most often due to a recipient's full mailbox or an excessively large email message. While it points to an issue on the receiving end, consistently encountering these errors can negatively impact your sender reputation and lead to broader deliverability challenges. By understanding the causes, accurately diagnosing the specific sub-type of 552 error, and implementing both immediate fixes and long-term prevention strategies like list hygiene and volume management, you can effectively manage this error and maintain a healthy email sending infrastructure.
