How to troubleshoot email deliverability issues to specific business domains?

Key findings

• Targeted issues: Deliverability problems affecting only a few specific domains often suggest a particular security vendor or internal filtering by those domains.
• Lack of bounces: When emails disappear without bounce-backs, it typically means they were accepted by the recipient's mail server but then filtered before reaching the inbox, often to a spam or quarantine folder.
• MX record analysis: Checking the recipient domains' MX (Mail Exchanger) records can reveal the mail service or security vendor they use, such as Proofpoint or Mimecast. This is a critical first step in diagnosis.
• Engagement data: Zero opens and clicks for these specific domains, while overall deliverability is good, reinforces the idea of targeted filtering rather than general sender reputation issues.
• Legitimate recipients: Even when recipients are legitimate and opted-in, security systems can still flag emails due to content, sender reputation, or specific rules. This isn't necessarily a sign of spam traps if the recipient organizations are active businesses.

Key considerations

• Recipient infrastructure: Understanding the recipient's email security stack, identified via MX records or EHLO responses, is crucial for tailored troubleshooting. You can gain insights from this article on troubleshooting email deliverability.
• Direct contact: Once a common security vendor is identified, contacting their postmaster or support can provide direct insights into why your emails are being filtered. Learn more about how to contact mailbox providers for deliverability issues.
• Recipient quarantine: Advise your client to ask their contacts at the problematic domains to check their spam or quarantine folders. Emails often land here without notification to the sender.
• Sender reputation: Even if overall good, specific domain-level reputation can be an issue. Regularly monitor your IP and domain reputation and perform deliverability tests.

Key opinions

• Domain-specific issues: Marketers frequently report issues with specific domains, especially in B2B contexts, suggesting that a universal deliverability strategy might not cover all edge cases.
• Recipient filtering: It is common for recipient organizations to employ stringent spam and security filters that can quarantine or silently drop emails, even from otherwise reputable senders.
• Industry commonality: If multiple domains in the same industry or geographical area experience issues, it often points to a shared security solution or common filtering policies.
• Postmaster communication: Reaching out to the recipient's postmaster or the security vendor's postmaster (e.g., Proofpoint) is a recognized step to diagnose and resolve such issues directly.

Key considerations

• Proactive checks: Before escalating, confirm standard email authentication protocols (SPF, DKIM, DMARC) are correctly configured. A useful tool is a free email testing tool.
• Content review: Even for legitimate emails, review content for anything that might trigger spam filters, such as excessive links, certain keywords, or poor formatting. Consider email testing best practices.
• Recipient engagement: Encourage recipients at the affected domains to whitelist your sending IP or domain, or to check their spam/quarantine. This is crucial as their security vendor might provide feedback directly to them about why messages are being blocked.
• Blocklist checks: Periodically check if your IP or domain is listed on any major blocklists or blacklists, even if it's a specific domain issue, as it can still contribute to the problem.

Key opinions

• MX record analysis: A fundamental first step is always to check the MX records of the problematic domains to identify their mail infrastructure, including the security vendors used.
• EHLO response check: Using telnet to port 25 on the MX servers and examining the EHLO response can further confirm the mail server software or security vendor in use.
• Quarantine function: Many enterprise security solutions (e.g., Proofpoint) utilize a quarantine feature where emails are held for review, not necessarily bounced, explaining the black hole effect.
• Direct communication: Reaching out to the security vendor's postmaster (e.g., Proofpoint) is often the most effective way to understand the specific filtering reasons and request whitelisting or delisting.
• Sender reputation nuances: Even with a good overall sender reputation, specific complaints or perceived issues by a particular security vendor can lead to targeted blocking or throttling. This is explored in guides like how to improve domain reputation.

Key considerations

• Spam trap possibility: While unlikely for known legitimate businesses, the possibility of spam traps (even less common ones) for inactive or repurposed domains should not be entirely dismissed without thorough investigation, as detailed in our guide on spam traps.
• Recipient's control: The ultimate control lies with the recipient's mail server and their security configurations. Solutions often require their intervention or cooperation.
• Proof of legitimacy: Be prepared to provide evidence of your email legitimacy, consent, and good sending practices when contacting security vendors or recipients.
• Consistent monitoring: Implement continuous deliverability monitoring to catch such issues early and identify trends that might indicate underlying problems with specific providers or security systems. More on this can be found in guides on email deliverability issues.

Key findings

• Authentication standards: Proper configuration of SPF, DKIM, and DMARC is critical for establishing sender legitimacy and is frequently cited as a primary factor for inbox placement. Failures can lead to targeted rejections.
• SMTP error codes: Documentation often details various SMTP error codes. A lack of bounce-backs (meaning no error code) typically implies acceptance by the recipient mail server, followed by internal filtering or quarantine.
• Mailbox provider policies: Many mailbox providers and security vendors publish specific policies or best practices for senders. Adhering to these is crucial, especially when dealing with targeted domains that may implement strict rules. For example, Outlook's new sender requirements are important to follow.
• Reputation building: Building and maintaining a positive sender reputation is an ongoing process, often influenced by complaint rates, spam trap hits, and engagement metrics, which can impact deliverability to specific organizations.

Key considerations

• Content guidelines: Review content against general spam filter guidelines (e.g., from RFCs or postmaster sites) to ensure it's not inadvertently triggering filters at the recipient end.
• List hygiene: Even with legitimate data, ensuring your list is clean and regularly updated helps avoid sending to invalid addresses that could be repurposed as spam traps or simply contribute to negative reputation. Consider diagnosing email deliverability issues.
• Feedback loops: Leverage feedback loops (FBLs) from major mailbox providers to receive complaints, even from specific domains, and promptly remove non-engaging subscribers.
• Domain-specific policies: Recognize that large organizations often have highly customized email security policies, which might override general internet standards or even cause throttling to Microsoft domains.