How to resolve Microsoft deliverability issues and IP blocks when using Salesforce Marketing Cloud?

Key findings

• IP blocks: A 5.7.1 error message with an S3150 code from Microsoft indicates a definitive IP block on the Salesforce Marketing Cloud IP range.
• Misleading replies: Microsoft support sometimes initially replies that there is nothing wrong with the IP, which can be interpreted as nothing wrong with their decision to block the IP.
• Persistence pays off: Despite initial denials, persistent follow-up and escalation with Microsoft support can eventually lead to the admission of a block and its mitigation.
• Content issues: Sending emails with non-secure HTTP images or links can trigger blocks, as Microsoft (Outlook, Hotmail, etc.) heavily penalizes such content. These are often discovered by digging into individual sends.
• Form confusion: There can be confusion between the delisting form for Office 365 (sender.office.com/Delist/Index) and the general consumer Microsoft postmaster support form (olcsupport.office.com), though the latter now serves both.

Key considerations

• Leverage SFMC Support: As the IP belongs to Salesforce Marketing Cloud, their delivery team should be the primary point of contact for managing and resolving the block. They often have direct channels to Microsoft. Learn more about resolving Microsoft domain deliverability issues from Salesforce.
• Obtain raw bounce messages: Always request the full, raw bounce message from Salesforce Support. This message contains the precise error codes and links that are vital for proper diagnosis and interaction with Microsoft.
• Direct communication with microsoft: Even with SFMC support, it's beneficial for the client to directly submit the Microsoft delisting form (olcsupport.office.com) and persist in communications, replying to every email from Microsoft.
• Review sending practices: While an IP block might seem technical, it's often rooted in sending practices. Ensure you are sending permission-based mail, sun-setting unengaged recipients, and avoiding problematic content (e.g., HTTP links). This is a common strategy when troubleshooting Outlook email deliverability issues. Blueshift also has 8 email deliverability strategies to fix Microsoft domain issues.
• Escalate effectively: If initial responses are unhelpful, explicitly request escalation from both Microsoft and Salesforce Support.

Key opinions

• Support limitations: Salesforce Marketing Cloud support, while helpful, may not always possess the deep deliverability expertise needed for complex Microsoft blocks, leading marketers to seek external advice.
• Error message analysis: The raw bounce message is crucial for understanding the specific reason for a block, such as a 550 5.7.1 S3150 code indicating an IP block. This data guides the next steps in troubleshooting.
• Content impact: Issues like sending images or links via HTTP instead of HTTPS are a frequent cause of blocks from Microsoft, even for legitimate senders. Marketers emphasize the need to audit content meticulously.
• Block bounce severity: A block bounced status is considered one of the worst types of bounces, signaling a significant reputation issue that requires immediate attention.
• IP warming: Even well-managed IP warm-ups in SFMC can face Microsoft issues, highlighting the unique challenges with this specific ISP.

Key considerations

• Consistent follow-up: Marketers advise consistently replying to Microsoft's emails, even after initial rejections, as persistence can eventually lead to resolution.
• Internal auditing: Conduct a deep dive into campaign content, especially for HTTP links or images, which are common triggers for Microsoft blocks. Tools like Litmus can help with content checks.
• Escalate through SFMC: Push Salesforce support to escalate the issue on their end, as they are typically better equipped to communicate with Microsoft regarding shared or private IPs. More information can be found on troubleshooting email deliverability in Salesforce Marketing Cloud.
• Data view analysis: Utilize SFMC's Bounce_DV to identify which emails or journeys triggered the high bounce rates, providing clues for remediation. This is key to diagnosing and fixing deliverability issues.
• Long-term outlook: Be prepared for a lengthy resolution process; some blocks can take months to clear without persistent effort.

Key opinions

• Interpreting replies: When Microsoft says no problem, it generally means the IP is blocked for a reason, and Microsoft stands by that decision. It requires the sender to fix the underlying issue before expecting mitigation.
• Persistence and escalation: Experts stress that senders must be persistent in replying to Microsoft and explicitly ask for escalation. This approach has led to re-evaluation and unblocking in many cases.
• Bounce message is key: A specific bounce code like S3150 is a smoking gun to push back on Microsoft and demand escalation, especially if it's a consistent block.
• ESP support gaps: It is frustrating when ESP support desks (like Salesforce) fail to guide clients to the correct Microsoft form or properly handle the issue, leading to unnecessary extra work for senders.
• 4XX errors: Transient 4XX errors from SFMC could indicate DNS resolution, networking, or MTA problems, or even a persistent (soft) block against the IP. These require thorough investigation by the ESP.

Key considerations

• Understand microsoft's forms: Be aware that Microsoft's delisting forms have evolved. While there was a separate one for Office 365, olcsupport.office.com is now the primary portal for various Microsoft domains. This can be critical when resolving deliverability issues with Microsoft domains.
• Persistent dialogue: As shared by an expert on Spam Resource, successful inbox delivery to Microsoft consumer mailboxes can be tricky and requires consistent monitoring and re-evaluation. Senders should continue to engage until a clear resolution or reason is provided. More details can be found in their ISP Deliverability Guide: Microsoft OLC.
• Self-service vs. support: While Microsoft provides tools like SNDS for insights, IP blocks on shared SFMC IPs often require Salesforce's intervention. However, for dedicated IPs, direct and persistent engagement with Microsoft by the client or their deliverability team is crucial, especially if IP warming issues arise.
• Root cause analysis: Focus on identifying the underlying cause of the block, whether it's list quality, content, or sending volume, rather than just seeking a quick delisting.
• Monitor SMTP conversation: While SFMC may not record when in the SMTP conversation a block occurs, understanding if it's after MAIL FROM, RCPT TO, or DATA can provide valuable diagnostic clues through iterative testing.

Key findings

• Official support channel: Microsoft's sender support documentation directs users to a specific form (olcsupport.office.com) for deliverability problems not covered in their FAQ.
• Bounce message guidance: Microsoft's bounce messages often contain direct links or explicit instructions for senders to follow when their emails are blocked, which should be the primary reference point.
• Policy compliance: Microsoft's documentation emphasizes that emails must comply with their policies and guidelines to ensure deliverability.
• Email authentication: Salesforce documentation (e.g., on Marketinet) highlights the importance of SPF, DKIM, and DMARC for improving email deliverability and avoiding spam filters in Marketing Cloud.
• IP warming importance: Salesforce Ben documentation stresses the importance of effective IP warming for new SFMC instances to build sender trust and maximize inbox placement, reducing the likelihood of blocks.

Key considerations

• Direct form usage: Always refer to the precise link provided in the bounce message or the official Microsoft sender support page to ensure the correct delisting form is used, as forms and URLs can change or redirect. This is key to resolving Microsoft email blocks when SNDS shows normal status.
• Understanding error codes: Familiarize yourself with Microsoft's bounce codes (e.g., 550 5.7.1) and their specific meanings to accurately diagnose issues.
• Authentication setup: Ensure that SPF, DKIM, and DMARC are correctly configured for your Salesforce Marketing Cloud sending domain. This is a foundational step for all email deliverability. For more info, check out Salesforce Email Authentication for Marketing Cloud.
• Proactive monitoring: Use tools like Microsoft's SNDS (Smart Network Data Services) to proactively monitor IP reputation and identify potential issues before they lead to severe blocks. This can prevent the need to troubleshoot why Salesforce emails are blocked.
• Implement best practices: Salesforce Trailhead advises on deliverability best practices and remediation tactics, which are fundamental to preventing deliverability issues across all ISPs.