Why are opted-in customers not receiving emails from my marketing campaign?

Key findings

• Silent filtering: Many B2B mail servers (like Microsoft 365 or Google Workspace) can accept emails but then quarantine them without sending a bounce message, making it appear as delivered by the ESP.
• Reputation impact: Poor sender reputation can lead to emails being silently dropped or sent to spam folders, even for opted-in recipients. This is particularly relevant when switching marketing automation platforms. We have a guide to improving your domain reputation if needed.
• Reporting gaps: ESPs typically report hard and soft bounces, but they might not capture instances where emails are accepted by the receiving server but then internally blocked or delayed before reaching the inbox.
• Recipient filters: Individual corporate email systems often have their own spam filters, firewalls, and security policies that can intercept emails based on content, sender history, or domain reputation, irrespective of initial acceptance. This is especially true for marketing emails.

Key considerations

• Verify delivery data: Do not solely rely on your ESP's 'delivered' status. Investigate logs for deferred messages or specific rejection messages even if they are not categorized as bounces. Learn more about factors affecting email deliverability.
• Isolate affected segments: Identify commonalities among customers not receiving emails, such as their mailbox provider (e.g., specific corporate domains using Microsoft or Google Workspace) or geographic location. This can pinpoint targeted filtering.
• Engage IT teams: For B2B clients, collaborate with their IT departments to check their spam filters, junk folders, and any quarantine systems. They might be able to release messages or safelist your sending domain.
• Authentication checks: Ensure your email authentication protocols (SPF, DKIM, DMARC) are correctly configured. Misconfigurations can lead to emails being silently dropped or blocklisted. Our guide on email authentication offers more details.

Key opinions

• Sales team reports: Sales teams often provide the initial alert about non-receipt, highlighting a critical gap between reported delivery and actual inbox placement, especially in B2B scenarios.
• B2B complexities: Corporate email systems are known for stricter filtering. They might drop emails without a bounce message based on the sender's reputation or recent sending habits.
• Distinguishing delivered vs. received: A common reporting gap means emails marked 'sent' or 'delivered' by an ESP might still be held in a recipient's inbound queue or quarantine, leading to non-receipt by the end user.
• Limited ESP data: Some ESPs (even large ones) may not provide granular enough data to diagnose these silent failures, only reporting hard and soft bounces.

Key considerations

• Deep dive into segments: It's vital to isolate the problematic segment and identify their common mailbox providers (e.g., mostly Microsoft or Google Workspace domains). We have a specific article on Microsoft inbox delivery issues.
• Recipient confirmation: While sales reports are valuable, verify with the clients directly or ask them to check spam/junk folders, and if possible, involve their IT team to look for quarantined messages.
• ESP logging: Demand more detailed delivery logs from your ESP, including any deferred statuses or specific SMTP responses that indicate a soft block or filtering. This is a crucial component of email deliverability troubleshooting.

Key opinions

• Deferred status: Emails can be severely delayed or permanently deferred by the mailbox provider, creating a reporting gap where they are not yet bounced but also not delivered to the inbox. They might eventually become bounces if the ESP's mail server gives up.
• ESP reporting accuracy: Some ESPs may misleadingly report messages as 'sent' when they were actually rejected by the recipient's server, leading to a false sense of delivery. This underscores the need for thorough log reviews.
• Mail filter quarantines: A common scenario is an email being accepted by the receiving mail server (resulting in a 250ok SMTP reply), but subsequently quarantined by internal mail filters, preventing it from reaching the user's mailbox. This is a typical blocklist action.
• Business vs. consumer domains: Silent filtering and quarantining are more prevalent in business or corporate email contexts compared to consumer domains managed by major providers like Google or Yahoo.

Key considerations

• Log examination: Always review your ESP's detailed logs for every email, looking for subtle indications like deferrals or rejection messages that don't immediately translate to a hard or soft bounce.
• Direct engagement with IT: Encourage clients to involve their IT teams to check quarantine folders, spam gateways, or internal blocklists where the emails might be held. These messages can often be released manually. Our guide on email blocklists explains more.
• Monitor deliverability metrics: Utilize tools like Google Postmaster Tools or other deliverability monitoring services to gain deeper insights into your sending reputation and potential filtering issues with major mailbox providers. This complements the data from your ESP.
• Proactive best practices: Adhere to strict opt-in processes and maintain a clean list to prevent deliverability problems before they start. Consult resources on boosting email deliverability rates.

Key findings

• SMTP 250 ok response: Receiving mail servers indicate acceptance with a 250 ok SMTP reply. However, this only signifies that the server has taken custody of the email, not that it has been delivered to the recipient's inbox. This is a common source of confusion in deliverability reporting.
• Post-acceptance filtering: After initial acceptance, internal mail filters, spam gateways, or security appliances can quarantine, discard, or route emails to junk folders based on their own rules and threat assessments, often without generating a bounce notification back to the sender.
• Deliverability definition: Deliverability is defined not just by successful delivery to the mail server, but by the email's final placement within the recipient's mailbox (inbox vs. spam/junk/quarantine). We have an article discussing email deliverability issues.
• Consent importance: Documentation consistently emphasizes that obtaining explicit permission (opt-in) from recipients is a foundational best practice for deliverability and compliance, though it doesn't eliminate all filtering challenges.

Key considerations

• Leverage detailed logs: Review comprehensive SMTP logs and delivery reports from your ESP for messages that show acceptance but no open or click activity, as these may indicate silent filtering. These logs often contain critical diagnostic information beyond basic bounce types.
• Understand ISP policies: Familiarize yourself with the specific policies of major ISPs and corporate mail providers regarding bulk email, sender reputation, and filtering practices. Different providers (e.g., Gmail, Microsoft) have varying thresholds.
• Sender authentication: Ensure all standard email authentication protocols (SPF, DKIM, DMARC) are correctly configured and aligned. Poor authentication is a primary reason for emails being flagged or dropped silently. Refer to guides on troubleshooting DMARC reports from Google and Yahoo.
• Content quality: Even with explicit opt-in, email content that triggers spam filters (e.g., excessive links, suspicious formatting, or certain keywords) can lead to silent blocking or spam folder placement.