What does the email error '552 5.2.0 sender rejected AUP#POL' mean and how to resolve it?
Matthew Whittaker
Co-founder & CTO, Suped
Published 7 May 2025
Updated 17 Aug 2025
6 min read
Encountering the email error '552 5.2.0 sender rejected AUP#POL' can be quite puzzling, especially since it's not always clearly documented by recipient mail servers. This bounce message signals a permanent failure in email delivery, meaning the recipient's server refused your message outright and won't try again. It’s categorized as a 552 SMTP error, which generally indicates a problem with the message size or the recipient's mailbox being full, but the additional 'AUP#POL' code points to a specific policy violation by the sender.
The 'AUP' part stands for Acceptable Use Policy, and 'POL' likely signifies 'Policy' or 'Policy Violation'. Essentially, the receiving server, often managed by internet service providers like Cox or Verizon, has determined that your email, or your sending practices, violate their established rules for email usage. This isn't usually about the content of a single email, but rather something systemic about the sender. Since it's a hard bounce, these messages will not be delivered and the recipient should be removed from your mailing list.
Understanding 552 error codes
The 552 SMTP error indicates a permanent failure. Unlike temporary errors, a 552 bounce means the message cannot be delivered in its current state and will not be retried by the sending server. This requires action from the sender to identify and fix the underlying issue.
While 552 errors are broadly associated with mailbox issues or excessive message sizes, the added 'AUP#POL' specific to sender rejection shifts the focus from the recipient's mailbox to the sender's compliance with policy.
Common causes of AUP#POL rejections
This error typically points to issues with the sender's domain or IP reputation, rather than specific email content. Internet Service Providers (ISPs) often employ sophisticated filtering systems, such as Cloudmark, to protect their users from unwanted mail. These systems analyze various signals to determine if an email or sender adheres to their acceptable use policies, which might not be explicitly published.
A common cause can be a new or recently migrated sending domain. If your domain is new, or if you've recently switched email platforms, the lack of established sending history and reputation can trigger policy filters. This is especially true if the IP address your emails are originating from has a poor reputation or is associated with senders of spam.
Incorrect or incomplete DNS records are another frequent culprit. Even if you've configured SPF, DKIM, and DMARC, problems with MX or PTR records can lead to rejections. For instance, if your domain's MX records point to unreachable hosts, or if the PTR record for your sending IP is misconfigured or points to a suspicious domain, recipient servers may reject your mail on policy grounds.
Diagnosing this error requires a systematic approach. First, examine the full bounce message for any additional clues beyond 'AUP#POL'. Sometimes, the ISP will provide a link to their error code documentation, even if the specific AUP#POL isn't explicitly listed. This can give you an idea of their general email policies. Remember that this is a 552 SMTP error, which indicates a permanent problem.
Next, thoroughly review your domain's DNS records, including SPF, DKIM, and DMARC. Ensure they are correctly configured and that your sending IP addresses are authorized. A mismatched PTR record, or one that points to a generic or suspicious domain, can also trigger these rejections, especially by sophisticated filters like Cloudmark's Cloudfilter. Verify that all MX records point to active and correct mail servers.
Pay close attention to the age and reputation of your sending domain and IP addresses. New domains often experience deliverability challenges as they build reputation. If your domain's PTR record points to a new domain or one associated with low-cost providers, it can be flagged by filters that see this as a common pattern used by spammers. This can lead to rejections, as seen with providers like Comcast Xfinity. Understanding your email domain reputation is crucial here.
Common mistakes
Ignoring bounce messages: Not analyzing the full error for specific clues or common patterns.
Poor list hygiene: Continuing to send to addresses that consistently bounce, signaling unwanted mail.
Incomplete DNS checks: Overlooking PTR or MX record misconfigurations.
Abrupt volume increases: Sending high volumes from new IPs/domains without proper warmup.
Best practices
Thorough bounce analysis: Pay attention to all details in the bounce message.
Maintain clean lists: Regularly remove invalid or unresponsive addresses.
Verify all DNS records: Ensure SPF, DKIM, DMARC, MX, and PTR are all correct.
Gradual IP warmup: Slowly increase sending volume on new IPs or domains.
Strategies for resolution and prevention
The most direct way to resolve this error is to contact the postmaster or abuse desk of the recipient's ISP. Provide them with the full bounce message, including headers, and explain your sending practices. While generic 'AUP#POL' messages can be frustrating, directly engaging with the ISP can sometimes lead to insights or even whitelisting.
Beyond direct contact, focus on strengthening your sender reputation and adhering to best practices. This includes warming up new IPs or domains gradually, maintaining a clean and engaged subscriber list, and ensuring your email content is relevant and anticipated by recipients. A strong and positive sending reputation is your best defense against such rejections. Learn how to improve domain reputation using Google Postmaster Tools.
Ensure your email authentication protocols—SPF, DKIM, and DMARC—are fully implemented and aligned. These records prove your legitimacy and help receiving servers trust your mail. A solid DMARC policy, especially, can signal to ISPs that you are serious about preventing abuse of your domain and can help prevent your emails from going to spam. If you're encountering persistent issues, consider consulting with a deliverability specialist.
Action
Description
Priority
Review bounce message
Look for specific details beyond the initial error code.
Reach out to their postmaster or abuse desk with full details.
As needed
Implement IP warmup
For new sending IPs or domains, send volume gradually.
Preventative
Views from the trenches
Best practices
Always check the full bounce message headers for clues, not just the initial error code.
Proactively monitor your domain and IP reputation on various blacklists (or blocklists) and with postmaster tools.
Ensure all DNS records, especially PTR records for sending IPs, are correctly configured and up-to-date.
For new sending infrastructure, implement a proper IP warming schedule to build trust gradually.
Common pitfalls
Misinterpreting '552' solely as a recipient mailbox issue instead of a sender policy violation.
Ignoring the specific 'AUP#POL' (or similar) codes and not investigating acceptable use policies.
Failing to contact the recipient's postmaster or abuse desk for specific insights and delisting requests.
Not considering the age and historical reputation of new domains or IP addresses.
Expert tips
Check for Cloudmark's presence. If the receiving mail server banners as Cloudmark, their filters are likely behind the 'AUP#POL' rejection.
Ensure MX records on your sending domain are valid and reachable, even lower priority ones, as some filters check them all.
The age of the domain in your PTR record can be a significant factor. Newer domains, particularly from 'low-cost' providers, are often viewed with suspicion.
If migrating platforms, recognize that each platform is a 'different sender' in the eyes of an ISP, and reputation must be built accordingly.
Marketer view
A marketer from Email Geeks says they migrated a client and despite correct SPF/DKIM/DMARC, they faced '552 5.2.0 sender rejected AUP#POL' errors specifically from Cox, CenturyLink, and other providers, noting that the 'AUP#POL' code was not listed in public error code documentation.
2023-09-27 - Email Geeks
Expert view
An expert from Email Geeks says that the 'sender rejected' portion of the error message implies the issue is specific to the sender's practices or domain, not necessarily the recipient's address.
2023-09-28 - Email Geeks
Final thoughts on AUP#POL rejections
The '552 5.2.0 sender rejected AUP#POL' error, while vague, provides critical insight into your sender reputation and compliance with ISP policies. It's a clear signal that the receiving server perceives a violation of its acceptable use policy, stemming from your sending domain, IP, or overall practices.
Proactive monitoring of your domain and IP health, meticulous DNS configuration, and consistent adherence to email best practices are your strongest defenses. By understanding the root causes and implementing effective resolution strategies, you can minimize these frustrating rejections and improve your overall email deliverability rates.
Cloudmark, to protect their users from unwanted mail. These systems analyze various signals to determine if an email or sender adheres to their acceptable use policies, which might not be explicitly published.
Cloudmark's Cloudfilter. Verify that all MX records point to active and correct mail servers.
Reach out to their postmaster or abuse desk with full details.
