What are the best practices for email deliverability when using SparkPost and Amazon SES, including reverse DNS, blacklist monitoring, and handling dedicated IPs?

Key findings

• Blacklist focus: While many blocklists are not highly influential, some, like Spamhaus and URIBL, carry significant weight and can severely impact deliverability. Monitoring these crucial ones is advised, even if others are less impactful.
• Reverse DNS importance: Properly configured reverse DNS (rDNS) records, matching your sending IP's hostname, are crucial for sender authentication and can prevent your emails from being flagged by some spam filters. This is particularly important for dedicated IPs.
• ESP responsibility: When using a third-party ESP like SparkPost or Amazon SES, they are primarily responsible for the technical setup and reputation management of their shared IP pools. For dedicated IPs, you will have more control and input.
• Beyond blacklists: Other key metrics, such as complaint rates, bounce rates, and inbox placement, are often more indicative of deliverability issues than general blocklist listings.

Key considerations

• Monitor your own IPs: If you are sending from your own data center IPs, or if your ESP's IPs appear in email headers, ensure you monitor their blacklist status and configure appropriate reverse DNS.
• Dedicated IP control: With dedicated IPs from your ESP, you have more control over aspects like reverse DNS configuration and the ability to build and maintain a unique sender reputation. This is a key benefit over shared IP pools.
• Metrics provided by ESPs: Leverage the metrics and dashboards provided by SparkPost and Amazon SES. These tools offer valuable insights into your sending performance and can help diagnose problems quickly. Consider SparkPost's delivery index as a key performance indicator. You can learn more about general email deliverability best practices from articles like Email Deliverability Best Practices: Top Tips for ROI.
• Multi-domain rDNS: When sending for multiple domains from your own IPs, ensure each domain's rDNS points to a relevant hostname (e.g., mail1.yourcorpdomain.com) rather than a generic one.

Key opinions

• Direct control: Many marketers are unsure about what aspects of IP and DNS configuration they need to manage versus what their ESP handles when not owning the Mail Transfer Agents (MTAs).
• Blacklist perception: There's a common belief that monitoring all blacklists is a critical activity, often seeing Spamhaus as the most significant, or the 'god' of blacklist services.
• IP header checks: Marketers frequently express the need to inspect email headers to identify which IPs are actually being used for sending and determine if they have control over their configuration.
• Seeking advice: There's a clear demand for practical advice on setting up DNS, particularly reverse DNS, when sending through third-party services like SparkPost and Amazon SES without direct server ownership.

Key considerations

• Understanding ESP roles: Marketers need clear guidance on the division of labor between their team and the ESP regarding IP management, DNS, and authentication (e.g., SPF, DKIM, DMARC), especially for third-party ESPs.
• Dedicated IP inquiries: For dedicated IPs, marketers should proactively engage with their ESPs to confirm and configure reverse DNS settings. This is a critical step for maintaining IP reputation.
• Header analysis: Learning how to interpret email headers to identify sending IPs and their corresponding rDNS is a valuable skill for marketers to confirm proper configuration.
• Beyond basic monitoring: While blocklist checks are quick, understanding the underlying factors affecting deliverability (e.g., engagement, spam complaints) is more effective. Marketers should focus on maintaining a healthy sender reputation, as discussed by Nylas in their deliverability tools overview.

Key opinions

• Blacklist utility: Many blacklists are considered largely useless, with few carrying significant weight (e.g., Spamhaus, URIBL). Focus should be on more impactful metrics.
• Reverse DNS as tidiness: Reverse DNS (rDNS) is primarily a matter of proper configuration and tidiness, though some filters may penalize generic or missing rDNS.
• ESP as primary handler: For ESPs like SparkPost and Amazon SES, they manage most setup and monitoring. Clients should primarily focus on ESP-provided metrics dashboards.
• Spamhaus dominance: Spamhaus is widely trusted and used due to its reasonable and consistently applied listing policies, giving it a significant and immediate impact on email delivery.

Key considerations

• Dedicated IP rDNS: If using dedicated IPs from an ESP, discuss rDNS setup with them, as it provides more influence over your IP's identity. Otherwise, you're in a shared pool with limited control.
• Check email headers: Verify which IPs appear in email headers if sending via your own IPs through an ESP, and ensure these have valid rDNS set up.
• Strategic blacklist monitoring: While not all blocklists are critical, monitoring key ones like Spamhaus is important. Other less impactful blocklists can act as a canary in a coal mine, indicating underlying problems that should be addressed regardless of direct delivery impact.
• Proactive delisting: Spamhaus will typically delist quickly and cheerfully once the root cause of the listing is resolved. Understanding how blacklists work and their policies can aid in swift resolution.

Key findings

• Reverse DNS configuration: Documentation consistently states that proper reverse DNS (PTR record) configuration is vital for IP authentication and is a key factor considered by receiving mail servers.
• Dedicated IP warm-up: For dedicated IPs, a gradual warm-up process is recommended to build a positive sending reputation with Internet Service Providers (ISPs) and avoid initial throttling or blocklisting.
• Authentication protocols: Strong email authentication (SPF, DKIM, DMARC) is foundational for proving sender legitimacy and preventing spoofing, which directly impacts deliverability and blacklist avoidance.
• Blacklist management: ESPs typically monitor major blacklists and implement automated processes for delisting. However, clients are often advised to mitigate underlying issues that lead to listings.

Key considerations

• Aligning rDNS with sending domains: For dedicated IPs, ensure the rDNS name aligns with the sending domain's branding (e.g., mail.yourdomain.com) for better trust signals.
• Monitoring deliverability metrics: Regularly review bounce rates, complaint rates, and open/click-through rates provided by the ESP to gauge IP and domain health, as these are strong indicators of deliverability issues.
• Proactive list hygiene: Maintain a clean mailing list by removing invalid or unengaged addresses to reduce hard bounces and spam complaints, which are major triggers for blacklistings.
• Compliance with policies: Adhere strictly to ESP acceptable use policies and anti-spam guidelines to prevent account suspension and maintain a good sending reputation. For example, Amazon SES outlines deliverability best practices in their FAQs.