← Back to Operational Notes Archive Engineering Operational Note · Published Production Engineering Memo · Technical Architecture · 14 min read Executive Summary Why Dedicated IPs Outperform Shared Pools at Volume At sufficient volume, dedicated IP addresses consistently deliver better inbox placement than shared pools. Architecture Scope Fleet Scale High-Volume Infrastructure Production Status 100% Inboxing […]
← Back to Operational Notes Archive Engineering Operational Note · Published Production Engineering Memo · Technical Architecture · 14 min read Executive Summary The Role of List Age in Deliverability Older lists generate more bounces, more complaints, and more spam trap hits than recently acquired lists. Architecture Scope Fleet Scale High-Volume Infrastructure Production Status 100% […]
← Back to Operational Notes Archive Engineering Operational Note · Published Production Engineering Memo · Technical Architecture · 14 min read Executive Summary Why Your Suppression List Is Your Most Valuable Deliverability Asset The suppression list — addresses that should never receive email again — is the most frequently under-managed component of email infrastructure. Architecture […]
← Back to Operational Notes Archive Engineering Operational Note · Published Production Engineering Memo · Technical Architecture · 14 min read Executive Summary Separating Cold, Bulk, and Transactional Traffic at the Infrastructure Level Cold email, promotional bulk, and transactional messages have fundamentally different quality profiles and reputation requirements. Architecture Scope Fleet Scale High-Volume Infrastructure Production […]
← Back to Operational Notes Archive Engineering Operational Note · Published Production Engineering Memo · Technical Architecture · 14 min read Executive Summary Inbox Placement Is a Lagging Indicator — And What to Monitor Instead Why inbox placement rates are a delayed signal, not a real-time view of email infrastructure health. Architecture Scope Fleet Scale […]
← Back to Operational Notes Archive Engineering Operational Note · Published Production Engineering Memo · Technical Architecture · 14 min read Executive Summary Soft Bounces That Become Hard Bounces: Time Thresholds and Suppression Logic A 4xx deferral is not a permanent failure — but a 4xx that persists across multiple campaigns eventually is. Architecture Scope […]
← Back to Operational Notes Archive Engineering Operational Note · Published Production Engineering Memo · Technical Architecture · 14 min read Executive Summary Understanding TLS Requirements and MTA-STS TLS encryption for email in transit became a practical requirement by 2022. MTA-STS extends this by enforcing TLS policy via DNS and HTTPS. Architecture Scope Fleet Scale […]
← Back to Operational Notes Archive Engineering Operational Note · Published Production Engineering Memo · Technical Architecture · 14 min read Executive Summary How Message-ID Structure Affects Deliverability The Message-ID header is more than a unique identifier. ISP filters use its format, domain, and structure as spam signals. Architecture Scope Fleet Scale High-Volume Infrastructure Production […]
← Back to Operational Notes Archive Engineering Operational Note · Published Production Engineering Memo · Technical Architecture · 14 min read Executive Summary The Anatomy of an SMTP Session: What Happens Between Send and Delivery Every email delivery is an SMTP conversation between two servers. Architecture Scope Fleet Scale High-Volume Infrastructure Production Status 100% Inboxing […]
← Back to Operational Notes Archive Engineering Operational Note · Published Production Engineering Memo · Technical Architecture · 14 min read Executive Summary DNS TTL Values and Their Impact on Email Authentication Changes The TTL on authentication DNS records determines how long a change takes to propagate globally. Architecture Scope Fleet Scale High-Volume Infrastructure Production […]