Summary
The Microsoft 550 5.7.515 'access denied' bounce, despite correct email authentication, typically indicates that Microsoft's Exchange Online Protection (EOP) or other internal systems have deemed the sending domain, IP address, or email content suspicious. The core issue often lies with sender reputation, which can be negatively impacted by factors like low recipient engagement, high spam complaints, sending to invalid email addresses, or a history of being associated with spam, including compromised accounts. Content-related triggers, such as suspicious links or spammy characteristics, can also lead to blockages. Additionally, Microsoft's own system glitches, like DNS lookup issues or even breaking valid DKIM keys, have been cited as contributing factors, and recipient-specific anti-spam policies can also override otherwise valid authentication.
Key findings
- Reputation, Not Just Authentication, is Key: Even when SPF, DKIM, and DMARC are correctly implemented and passing, Microsoft 550 5.7.515 'access denied' bounces frequently occur due to poor sender IP address or domain reputation. This includes factors like low recipient engagement, sending to invalid lists, high complaint rates, or being on an internal or public blocklist.
- Content and Behavioral Filtering: Microsoft's anti-spam engine, Exchange Online Protection (EOP), can block emails based on message content, sender behavior patterns, or the message's Spam Confidence Level (SCL), even if authentication is valid. Suspicious links, malformed HTML, or other characteristics can trigger these filters, leading to access denial.
- Compromised Accounts and Spam Activity: A common cause for this error is a sending account or IP address that has been compromised and used to send spam. Microsoft's systems are designed to detect such unusual activity, leading to blocks to protect recipients, regardless of prior authentication success.
- Microsoft's Internal Blocklists: Microsoft maintains internal blocklists for IP addresses and domains that have generated a high volume of spam complaints from Office 365 users or appeared on common public blocklists. Getting placed on these internal lists can lead to persistent 'access denied' errors, which are challenging to resolve.
- Potential Microsoft System Issues: Some instances of this error have been linked to temporary issues on Microsoft's side, such as DNS lookup problems or situations where their servers inadvertently break perfectly valid DKIM keys. Resending the email can sometimes resolve a small number of these specific failures.
- Recipient Policy Overrides Authentication: The 550 5.7.515 error can also stem from the recipient organization's strict anti-spam policies or internal rules within Microsoft 365 that block the sender, often based on the message's SCL, emphasizing that recipient-side configurations can override a sender's authentication status.
Key considerations
- Check Sender Reputation and IP Status: Regularly monitor your IP address and sending domain reputation with Microsoft and on public real-time blocklists (RBLs). A poor reputation, high spam complaints, or presence on blocklists often triggers these errors, even with proper authentication. Sending from dynamic IP addresses can also be a red flag for Microsoft.
- Review Email Content and Quality: Scrutinize email content for anything that might trigger spam filters, such as suspicious links, malformed HTML, excessive images, or spammy keywords. Microsoft's anti-spam engine (Exchange Online Protection) can block messages based on content or other behavioral patterns, irrespective of authentication status.
- Verify Account Security and Sending Habits: Investigate whether the sending account or domain has been compromised and used to send spam. Microsoft's systems quickly detect unusual activity and may block future sends. Also, avoid sending to unknown or stale user lists, as high bounce rates and low engagement negatively impact sender reputation.
- Inspect Authentication Alignment and Integrity: While authentication might appear correct, ensure SPF and DKIM records are perfectly aligned with your FROM domain. Use tools like aboutmy.email to perform test sends and identify any subtle authentication issues, noting that Microsoft has been observed to sometimes break valid DKIM keys or experience DNS lookup problems.
- Review Microsoft 365 Policies: Examine the recipient's organization's strict anti-spam policies or internal rules within Microsoft 365, which might be blocking your messages based on the Spam Confidence Level (SCL). For your own sending, review outbound spam filter configurations in Microsoft 365 to ensure legitimate emails aren't being erroneously flagged.
- Monitor for Async Bounces and Microsoft-Side Issues: Check if bounces are async or delayed, which could indicate forwarded messages where SPF failures might be expected. Be aware that Microsoft has experienced intermittent DNS lookup issues and delays in delivery status notifications, suggesting some bounces could be due to temporary system glitches on their end; resending might resolve a small number of failures.
What email marketers say
15 marketer opinions
The Microsoft 550 5.7.515 'access denied' bounce, despite correct email authentication, primarily signals a deeper issue with sender reputation or content quality as perceived by Microsoft's systems. While authentication like SPF, DKIM, and DMARC might be valid, a poor reputation due to factors such as low recipient engagement, high complaint rates, or sending to unverified lists can lead to blocks. Email content, including suspicious links or spammy characteristics, can also trigger these filters. Other significant causes include compromised sending accounts, shared IP addresses associated with spam, or placement on Microsoft's internal blocklists. It's also been noted that Microsoft's own system glitches, such as DNS lookup problems or issues with DKIM processing, can contribute to these errors, and even the sender's own Microsoft 365 outbound spam policies might inadvertently block legitimate emails.
Key opinions
- Reputation is Paramount: Beyond correct SPF, DKIM, and DMARC authentication, a poor sender IP or domain reputation with Microsoft is the primary cause of 550 5.7.515 errors. This reputation is severely impacted by low recipient engagement, high complaint rates, sending to stale or unverified lists, and high bounce rates.
- Content as a Trigger: Even with perfect authentication, the email's content itself- including suspicious links, malformed HTML, or excessive images- can trigger Microsoft's spam filters, resulting in a denial because the message is deemed unsafe or spammy.
- Compromised Accounts and Shared IP Blacklisting: A common reason for these errors is a recently compromised sender account or a shared IP address being used by another sender for spam, which can lead to the IP being blacklisted by Microsoft's systems.
- Microsoft's Internal Scoring and Blocklists: The error can signify that the sender's IP or domain is on an internal Microsoft blocklist, or that their internal scoring mechanisms have assigned a low trustworthiness score due to past issues or spam complaints. Sending from dynamic IP addresses is also heavily scrutinized due to their association with spam.
- Microsoft System Glitches and DKIM Handling: Microsoft has admitted to experiencing intermittent DNS lookup issues and delivery delays, which can contribute to these bounces. There are also instances where Microsoft's systems appear to improperly process or 'break' valid DKIM signatures despite them passing tests elsewhere.
- Sender's Own Microsoft 365 Configuration: In some cases, the error can stem from the sender's own outbound spam filter configuration within Microsoft 365, which might be erroneously flagging legitimate emails as spam and blocking their delivery.
- Asynchronous Bounces and Forwarded Messages: Delayed or asynchronous bounces can indicate forwarded messages where SPF failures would be expected, distinguishing these from direct authentication failures.
Key considerations
- Proactive Reputation Management: Continuously monitor your sending IP and domain reputation. Focus on maintaining high engagement, minimizing bounce rates, and avoiding spam complaints to build and preserve a positive standing with Microsoft. Be cautious when sending from dynamic IP addresses, as they are heavily scrutinized.
- Thorough Content Review: Before sending, meticulously review email content for anything that might be flagged as spam, such as suspicious links, problematic HTML, or overly promotional imagery. Microsoft's Exchange Online Protection (EOP) can trigger blocks based on content, regardless of authentication.
- Security and IP Vigilance: Regularly audit sender accounts for any signs of compromise, as a recently compromised account sending spam can lead to immediate access denial. If using shared IPs, verify their reputation and ensure other senders are not causing issues.
- Advanced Authentication Checks: Utilize diagnostic tools like aboutmy.email to perform detailed tests of your email authentication, paying close attention to SPF and DKIM alignment with your FROM domain. Microsoft's systems can sometimes be particular about DKIM or experience DNS lookup issues.
- Review Microsoft 365 Outbound Policies: If you are using Microsoft 365 to send, inspect your own outbound spam filter policies. Incorrect configurations might inadvertently flag and block your legitimate outgoing emails, leading to access denied bounces.
- Understand Bounce Types and Microsoft Issues: Differentiate between immediate and asynchronous, or delayed, bounces. Delayed responses can provide clues, especially regarding forwarded messages where SPF failures might be expected. Be aware that some issues might stem from temporary Microsoft system problems, such as DNS lookup glitches or general delivery delays.
Marketer view
Marketer from Email Geeks suggests using aboutmy.email to send a test email to identify any authentication issues, particularly those related to alignment.
14 Jul 2024 - Email Geeks
Marketer view
Marketer from Email Geeks inquires if SPF and DKIM are aligned with the FROM domain and later clarifies that a majority of his customers, using various on-premise and ESP platforms, are not experiencing this specific Microsoft bounce issue.
28 Oct 2021 - Email Geeks
What the experts say
3 expert opinions
The core problem behind Microsoft 550 5.7.515 "access denied" bounces, even when email authentication is correctly configured, often boils down to negative sender reputation. This can stem from high spam complaint rates, poor list hygiene leading to spam trap hits, or general content issues that trigger Microsoft's filters. Furthermore, a sending IP address or domain might be placed on internal Microsoft blocklists, making deliverability challenging. In some less frequent cases, the issue could even be attributed to temporary Microsoft-side system glitches, such as DNS lookup failures or improper handling of valid DKIM keys.
Key opinions
- Reputation & Internal Blocks: Even with perfect SPF, DKIM, and DMARC, a major cause of Microsoft's 550 5.7.515 access denied errors is a poor sender reputation, often leading to the sending IP or domain being placed on internal Microsoft blocklists due to high spam complaints or presence on public blocklists.
- Content & List Quality: Email content deemed problematic, such as containing spam trigger words or suspicious links, along with poor list hygiene including high spam complaints and hitting spam traps, directly impacts sender reputation and can lead to Microsoft 550 errors.
- Microsoft System Glitches: Less frequently, these bounces may be due to temporary glitches on Microsoft's end, like faulty DNS lookups or their systems misinterpreting valid DKIM keys, suggesting that for a small number of failures, re-sending the email might resolve the issue.
Key considerations
- Monitor Sender Reputation: Continuously monitor your sender reputation by keeping complaint rates low, ensuring your email lists are clean of inactive or trap addresses, and checking your IP and domain against public blocklists to avoid Microsoft 550 bounces.
- Content & Auth Integrity: Diligently review email content for potential spam triggers. While ensuring correct SPF, DKIM, and DMARC authentication is essential, be aware that Microsoft can sometimes have issues with valid DKIM keys or DNS lookups, so re-sending for a small number of failures can sometimes help.
- Delisting from Microsoft: If persistent 550 5.7.515 bounces indicate an internal Microsoft blocklist, be prepared for a challenging delisting process that often requires direct engagement with Microsoft support or consistent, high-quality sending to gradually improve your sender reputation.
Expert view
Expert from Email Geeks suggests the issue could stem from a bad DNS lookup that might be resolved by resending the email. He also notes that Microsoft has been observed to break perfectly valid DKIM keys, possibly due to server configuration issues, or problems with domain administration under O365, advising to re-send for a small number of failures.
6 Aug 2022 - Email Geeks
Expert view
Expert from Spam Resource explains that a Microsoft 550 error, including "access denied" bounces, often indicates that your IP or domain has been blocked by Microsoft. This can occur even with correct authentication due to poor sender reputation, high spam complaints, problematic content, or hitting spam traps. The article advises checking sender reputation, monitoring complaint rates, reviewing content for spam trigger words, and ensuring lists are clean of inactive or trap addresses.
18 Jun 2023 - Spam Resource
What the documentation says
3 technical articles
The Microsoft 550 5.7.515 'access denied' bounce, despite correct authentication, consistently indicates that Microsoft's robust anti-spam defenses, primarily Exchange Online Protection (EOP), have flagged the message. This often stems from a compromised sending account or IP address engaged in suspicious activity, leading to inclusion on Microsoft's internal blocklists. The error can also arise from the recipient's organization having stringent anti-spam policies or internal rules that block messages based on their Spam Confidence Level (SCL), even if authentication is valid. Ultimately, it signifies that message content, sender reputation, or behavioral patterns are deemed suspicious by Microsoft's advanced filtering systems.
Key findings
- Compromised Accounts & IP Blacklisting: This error frequently indicates that a sending account or IP address has been compromised and is sending spam, or that the sending server has been placed on a Microsoft block list due to suspicious activity.
- Recipient Policy & SCL Blocks: The 550 5.7.515 error can occur when a recipient's organization has a strict anti-spam policy or an internal rule that blocks the sender based on the message's Spam Confidence Level (SCL), even if email authentication is correctly configured.
- EOP Content & Reputation Filtering: Exchange Online Protection's (EOP) anti-spam engine, often with sub-codes like AS(S2000), will block messages if their content, the sender's reputation, or other behavioral patterns are deemed suspicious, overriding otherwise correct authentication.
Key considerations
- Check for Compromised Sources: Thoroughly investigate whether the sending account or IP address has been compromised and is inadvertently sending spam. Proactive monitoring for unusual sending activity is crucial to avoid being placed on Microsoft's block lists.
- Assess Content for SCL Impact: Review your email content for elements that might elevate its Spam Confidence Level (SCL), even with proper authentication. This includes scrutinizing links, attachments, and overall message quality, as recipient policies can block based on SCL.
- Grasp EOP's Deep Filtering: Understand that Microsoft's Exchange Online Protection (EOP) utilizes a sophisticated anti-spam engine that evaluates content, sender reputation, and behavioral patterns. Correct authentication alone is insufficient if these other factors trigger a block, emphasizing the need for continuous deliverability optimization.
Technical article
Documentation from learn.microsoft.com explains that the 550 5.7.515 error often indicates that the sending account or IP address has been compromised and is sending spam, or that the sending server is on a Microsoft block list due to suspicious activity. It advises checking for compromised accounts and reviewing the sender's reputation.
16 May 2025 - learn.microsoft.com
Technical article
Documentation from Microsoft Q&A, shared by a Microsoft Support Engineer, states that the 550 5.7.515 error can occur when the recipient's organization has a strict anti-spam policy or an internal rule that blocks the sender based on the Spam Confidence Level (SCL) of the message, even if authentication passes. This often points to the message content or sender's reputation being flagged.
12 Sep 2022 - Microsoft Q&A
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