Why am I getting a Microsoft bounce message and how can I resolve it?
Michael Ko
Co-founder & CEO, Suped
Published 30 Jun 2025
Updated 19 Aug 2025
5 min read
Receiving bounce messages from Microsoft servers can be incredibly frustrating. These non-delivery reports (NDRs) indicate that your email could not be delivered to a recipient using a Microsoft-hosted service, such as Outlook.com, Microsoft 365, or Exchange Online. Understanding these messages is the first step in resolving the underlying issues and ensuring your emails reach their intended destination.
Each bounce message contains vital clues, often in the form of a specific error code and a descriptive explanation. Decoding these details will pinpoint why your message was rejected, helping you diagnose whether the problem lies with your sending infrastructure, the recipient's configuration, or other factors. This guide will walk you through common Microsoft bounce scenarios and provide actionable steps to resolve them.
Deciphering Microsoft bounce codes
Microsoft bounce messages typically include an SMTP error code, often starting with "5xx," which indicates a permanent failure. These codes provide a granular view of the issue. For instance, a common code might point to an invalid recipient, while another could signify a sender reputation problem or a security restriction.
It is crucial to read the entire bounce message, not just the code. The accompanying text often provides a more detailed explanation and sometimes even suggests specific actions you can take. These explanations are vital for accurate diagnosis and efficient troubleshooting.
Many delivery issues are explained in Microsoft's own documentation on non-delivery reports. Understanding these common codes and their meanings is the first step in effectively resolving email delivery challenges to Microsoft domains.
Error Code
Description
Likely Cause
550 5.1.1 (or 5.1.x)
Recipient address rejected: User unknown or Invalid recipient
Invalid or non-existent email address, often a typo.
You don't have permissions to send to this email address.
Sender lacks permission to send to a specific recipient, often a restricted distribution group.
550 4.4.7
Message expired: recipient server did not respond
Temporary network issue, mail server offline, or aggressive anti-spam filtering.
552
Mailbox full or Message too large
Recipient's mailbox quota exceeded or email size (including attachments) is too large.
Root causes of Microsoft email bounces
To effectively resolve Microsoft bounce messages, it's essential to understand their root causes. These can broadly be categorized into sender-related issues or recipient-side configurations. Addressing the symptoms without understanding the cause will only lead to temporary fixes or recurring problems.
Sender-side problems often revolve around your email sending practices and infrastructure. This includes your sender reputation, which Microsoft heavily relies on to filter emails, and the proper configuration of email authentication protocols. If your reputation is low or your authentication records are misaligned, Microsoft servers are more likely to reject your mail, classifying it as potential spam or unauthorized.
Conversely, recipient-side issues stem from the Microsoft 365 or Exchange environment of the recipient. This could be as simple as an invalid email address or a full mailbox. More complex issues arise from restrictive internal policies, security settings, or specific configurations on the recipient's end that prevent external senders from delivering mail.
Sender-related issues
Poor reputation: Sending from a low-reputation IP address or domain can lead to rejection.
Mailbox full: The recipient's inbox has reached its storage limit.
Recipient policies: The recipient's organization has strict email receiving rules, such as disallowing external sending to certain groups or individuals.
Firewall/Antivirus: Aggressive security settings on the recipient's network blocking incoming mail.
Diagnosing and resolving Microsoft bounce messages
When you receive a Microsoft bounce message, the first step is always to examine the full bounce message text. Look for specific error codes like 550 5.7.1 or 550 5.1.1 as they often direct you to specific Microsoft support articles or provide a clear reason for the failure.
If the bounce indicates an invalid recipient, double-check the email address for typos. Even if it looks correct, there might be a subtle error, or the recipient's account might no longer exist. You can try sending a test email from a different, well-reputed email service (like a personal Gmail account) to see if it delivers, helping you rule out issues specific to your sending system.
Email authentication is a critical area for Microsoft deliverability. Ensure your domain's SPF, DKIM, and DMARC records are properly configured and aligned. Microsoft aggressively filters emails that fail these checks, especially with stronger DMARC policies. You can find Microsoft's guidance on 550 5.7.1, which often relates to authentication or blocklisting.
Key checks for email authentication
SPF: Verify your SPF record includes all authorized sending IP addresses and domains. If not, Microsoft may reject your emails.
DKIM: Confirm your DKIM signature is valid and correctly aligned with your domain. A failed DKIM can severely impact deliverability.
DMARC: Check your DMARC policy. A p=reject policy can cause emails to bounce if SPF or DKIM fail, leading to stricter enforcement. See how to fix DMARC issues in Microsoft 365.
Advanced strategies for prevention
Proactive measures are crucial to minimize Microsoft bounce messages. Regularly monitor your sender reputation using tools like Google Postmaster Tools or Microsoft SNDS. A strong reputation ensures your emails are less likely to be flagged as spam or rejected outright. Regularly clean your email lists to remove invalid or inactive addresses, which helps maintain a low bounce rate and avoids spam traps.
Implementing robust email authentication is non-negotiable. Moving your DMARC policy from p=none to a stricter p=quarantine or p=reject helps protect your domain from spoofing and builds trust with major mailbox providers like Outlook.
Finally, proactively monitor your IP and domain against public blacklists and blocklists. Being listed can severely hinder deliverability, not just to Microsoft, but across all providers. If you find yourself on a blacklist (blocklist), follow the delisting procedures promptly to restore your sending reputation.
Avoid getting blocklisted
High complaint rates: Excessive spam complaints from recipients can quickly lead to your IP or domain being blocklisted.
Malware/Phishing: If your email infrastructure is compromised, it could be used for malicious purposes, resulting in immediate blocklisting by Microsoft.
Volume spikes: Sudden, uncharacteristic surges in email volume can trigger spam filters and lead to temporary or permanent blocks.
Views from the trenches
Best practices
Regularly check bounce messages for specific error codes to quickly diagnose issues.
Ensure your domain's email authentication records (SPF, DKIM, DMARC) are correctly configured and aligned.
Implement a robust list cleaning process to remove invalid or inactive email addresses.
Proactively monitor your IP and domain reputation to identify and address issues before they impact deliverability.
Common pitfalls
Ignoring bounce messages, which can lead to continued sending to bad addresses and reputation damage.
Assuming a legitimate email address is a permanent hard bounce without further investigation.
Not differentiating between temporary and permanent bounce reasons in your email system.
Failing to address an ESP's (Email Service Provider's) improper bounce handling, which can skew deliverability data.
Expert tips
Sometimes, an email address that looks individual might be a restricted group or alias on the recipient's side, leading to permission issues.
When troubleshooting, try sending through a different email system (MTA) like a personal Gmail account to rule out local sending issues with your primary system.
If you observe sporadic successful deliveries to an address that also frequently bounces, it may indicate a misconfiguration on the recipient's Exchange server or an issue with your ESP's bounce processing.
Be wary of 'phantom clicks' or skewed data from your ESP; these can mask underlying deliverability problems.
Marketer view
Marketer from Email Geeks says: I often see a bounce message stating 'Your message can't be delivered because you do not have permissions to send to this email address.' It's common with smaller business domains.
2020-01-30 - Email Geeks
Marketer view
Marketer from Email Geeks says: This type of permission-related bounce message is typically from Microsoft, especially when trying to email a group from outside the organization.
2020-01-30 - Email Geeks
Navigating Microsoft email bounces
Microsoft bounce messages, while initially a hindrance, are valuable feedback for your email program. Each non-delivery report provides a direct reason for why your message failed to reach its recipient, offering clear guidance toward a resolution.
By systematically analyzing the error codes and descriptive text, addressing common issues such as incorrect email addresses or authentication failures, and maintaining good sender practices, you can significantly improve your email deliverability to Microsoft-hosted inboxes.
Microsoft's Exchange Online Protection (EOP).
Outlook.
