Summary
Even with a good sender reputation and the absence of apparent errors, email delivery delays can arise from a multitude of factors both on the sending and receiving ends. These include greylisting, recipient server throttling, internal organizational delays, spam filtering processes, sudden changes in sending patterns, personalized email content affecting scan times, and deferrals due to security checks. Recipient engagement plays a crucial role, with low engagement potentially leading to throttling. Technical aspects like DKIM replay and the use of IronPort appliances for reputation analysis also contribute. Network issues, server overload, transport rules, and prioritization algorithms can further affect delivery times. Consequently, identifying the root cause requires a comprehensive examination of sending practices, server configurations, and recipient-side factors.
Key findings
- Greylisting & Deferrals: Receiving servers may use greylisting or deferrals for security, temporarily rejecting emails.
- Server Throttling: Recipient email clients can throttle messages to manage server load, especially with free services.
- Internal Delays: Delays within recipient organizations, particularly large ones, can occur.
- Spam Filtering & Security Checks: Spam filters, security checks, and prioritization algorithms cause delays, especially for new senders.
- Sending Volume & Patterns: Sudden changes in sending patterns or volume can trigger deliverability issues.
- Personalized Content: Personalized content may slow down spam filter scanning.
- Recipient Engagement: Low recipient engagement can lead to throttling.
- DKIM Replay: DKIM replay can cause delays.
- Network & Server Issues: SMTP servers may delay messages due to network issues or overload.
- Appliance Processing: Appliances like IronPort use reputation analysis which can introduce delays.
- Transport Rules: Exchange Online delays can be caused by transport rules.
Key considerations
- Monitor Bounce Logs: Check bounce logs for rejections to identify potential problems.
- Improve Engagement: Focus on improving recipient engagement to avoid throttling.
- Sending Consistency: Maintain consistent sending patterns and avoid sudden volume increases.
- Content Testing: Test different content types to identify delays.
- Review Sending Practices: Evaluate recent changes to sending practices which may have triggered increased filtering.
- Track Logs: Utilize message tracking logs to follow the delivery path of emails.
- Retry Delivery: Ensure sending servers are retrying delivery for a certain period when initial attempts fail.
What email marketers say
9 marketer opinions
Even with a good sender reputation and the absence of apparent errors, email delivery delays can stem from various factors on both the sending and receiving sides. These include greylisting, recipient server throttling, internal organizational delays, spam filtering processes, sudden changes in sending patterns, and even personalized email content affecting scan times. Recipient engagement levels also play a vital role, as low engagement can lead to throttling by ISPs.
Key opinions
- Greylisting: Receiving servers might use greylisting, temporarily rejecting emails from unknown senders, causing delays.
- Server Throttling: Recipient email clients or service providers may throttle incoming messages to manage server load or prevent abuse, especially common with free email services.
- Internal Delays: Delays within the recipient's organization, especially large companies, can cause perceived delivery delays.
- Spam Filtering: Spam filtering processes, security checks, and prioritization algorithms can delay emails, particularly from new or infrequent senders.
- Sending Patterns: Sudden spikes in sending volume or changes in sending patterns can trigger scrutiny from ISPs, leading to temporary deliverability issues.
- Personalized Content: Personalized email content may trigger delays as spam filters take longer to scan individual email messages.
- Low Engagement: Low recipient engagement (opens, clicks, replies) can lead to throttling and delays, even with a good sender reputation.
- DKIM Replay: Delayed email delivery could be a result of DKIM replay, although more information is needed to confirm.
- Deferrals: Experiencing deferrals, check bounce logs for temporary and permanent rejections.
Key considerations
- Monitor Bounce Logs: Regularly check bounce logs for temporary and permanent rejections to identify potential issues.
- Engage Recipients: Focus on improving recipient engagement metrics (opens, clicks, replies) to avoid throttling.
- Sending Volume: Avoid sudden spikes in sending volume and maintain consistent sending patterns.
- Content Testing: Test different types of email content to determine if personalized content is causing delays.
- Server-Side Issues: Recipient server may be experiencing high loads.
Marketer view
Email marketer from Email Geeks mentions that delayed email delivery could be a result of DKIM replay, although more information is needed to confirm.
31 Oct 2023 - Email Geeks
Marketer view
Email marketer from EmailGeek Forum shares that internal delays within the receiving organization (especially with large companies) can cause perceived delivery delays, even if the email was technically accepted quickly by the receiving server.
8 Jan 2025 - EmailGeek Forum
What the experts say
1 expert opinions
Even with a good sender reputation and no apparent errors, email delays can occur because recipient servers may defer emails while performing additional security checks. It's important to review recent changes to sending practices that might have triggered this deferral behavior.
Key opinions
- Deferral: Recipient servers may defer emails for additional security checks.
- Trigger: Changes in sending practices can trigger deferral behavior.
Key considerations
- Review Practices: Check recent changes to sending practices to identify potential triggers for deferrals.
- Monitor: Monitor email delivery times and bounce rates to identify potential issues.
Expert view
Expert from Word to the Wise shares that delays can result from emails being deferred and held by recipient servers that may be performing additional security checks. She suggests checking your sending practices to identify any changes that may have triggered this behavior.
3 Apr 2022 - Word to the Wise
What the documentation says
5 technical articles
Email delivery delays, despite a good reputation and absence of errors, can be attributed to various factors on the receiving end. SMTP servers might delay messages due to network issues, server overload, or greylisting, which is a standard spam-fighting technique. Email providers like Gmail, Exchange Online, and systems using IronPort appliances implement spam filtering, security checks, prioritization algorithms, transport rules, and server-side processing that can introduce delays, especially for new or infrequent senders.
Key findings
- Network Issues: SMTP servers might delay messages due to temporary network issues.
- Server Overload: Receiving servers can be overloaded, leading to delayed acceptance or delivery.
- Greylisting: Greylisting is a technique where legitimate emails are delivered after a delay.
- Spam Filtering: Providers use spam filtering and security checks which can delay messages.
- Prioritization: Email prioritization algorithms can delay messages from new senders.
- Transport Rules: Exchange Online delays can be caused by transport rules.
- Server-Side Processing: Server-side processing can introduce delays.
- Sophisticated Analysis: IronPort appliances use reputation analysis that can introduce delays.
Key considerations
- Retry Delivery: Sending servers should retry delivery for a certain period as per standard practice.
- Track Logs: Use message tracking logs to understand the path and processing time of emails (e.g., Exchange Online).
- Monitor Reputation: Be mindful of sudden sending reputation changes that may trigger filtering.
Technical article
Documentation from Google explains that Gmail can delay emails due to spam filtering processes, security checks, and prioritization algorithms. Emails from new or infrequent senders may experience longer delays while Gmail assesses their legitimacy.
9 Jul 2021 - Google Workspace Admin Help
Technical article
Documentation from Cisco highlights that IronPort appliances, commonly used in enterprise environments, employ sophisticated spam filtering and reputation analysis that can introduce delays as emails are scanned and processed.
24 May 2023 - Cisco
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