Operations

• Content and Design for Deliverability

  Content-level filtering factors — spam-trigger-word myths vs reality, image/text balance, link practices, headers, subject lines, Gmail tabs, and engagement-optimizing design.

• Deliverability Metrics and Benchmarks

  Concrete definitions of bounce, complaint, and engagement metrics, with the numeric thresholds major ESP guides consider healthy — and the corrective actions when a metric goes out of range.

• Delivery Events and Diagnostics

  The delivery-event taxonomy an ESP/MTA emits (processed, deferred, delivered, bounce, blocked, dropped, spam-report, open, click), plus insights reporting, delay diagnosis, and engagement-quality scoring — the instrumentation layer beneath the troubleshooting playbooks.

• Delivery Troubleshooting Playbooks

  Symptom-driven decision procedures (symptom → hypothesis → discriminating test → fix) for the four delivery failure modes — not delivered, delayed, in spam, missing — with per-provider branches and a scenario library.

• List Hygiene and Sunset Policies

  How to acquire addresses safely, validate them at signup, handle bounces and complaints operationally, and sunset unengaged recipients before they hurt reputation.

• Mandated and Regulatory Email

  How to send legally required bulk notices — breach notifications, recalls, policy changes — to entire databases (including suppressed and unengaged addresses) without destroying sender reputation.

• MTA Delivery Tuning

  Outbound queue theory and delivery tuning as a discipline — queue-age diagnosis, per-destination concurrency and rate shaping, connection reuse, adaptive backoff and dead-site detection, scheduler fairness, and bounce-driven traffic-shaping automation.

• Non-Human Interactions (NHI) and Email Metrics

  M3AAWG's Nov 2020 study of automated "bot clicks" from security scanners — <10% B2C vs 20–80% B2B click/open inflation, why filtering NHI out is unreliable, and the practices that reduce it.

• Open and Click Tracking Mechanics

  How ESPs actually count opens and clicks — pixel and link-wrapping mechanics across Pardot, Eloqua, Bird, Customer.io, and Braze — with unique-vs-total definitions, the "read rate" concept, and what each metric does and doesn't prove.

• Per-Provider Tuning Baselines

  Community-maintained per-provider MTA shaping baselines — connection limits, messages per connection, rates, TLS requirements, and automated-throttle rules — from the KumoMTA shaping files, attributed and dated.

• Placement Measurement Methodology

  How inbox placement is actually measured — seed lists, subscriber panels, pixel/read-rate telemetry, and mailbox-provider dashboards — and the systematic bias each method carries, including Google Postmaster Tools' no-data blind spots.

• Reputation Incident Recovery

  The recovery runbook after a compromise or reputation collapse — securing the account, purging queues, rebuilding suppressions, re-warming vs cold warm-up, reading deferrals during recovery, automated warmup schedules as vendors implement them, and when to replace vs rehabilitate an IP or domain.

• Reputation Monitoring and Remediation

  How senders monitor IP and domain reputation in practice — blocklist monitoring, seed/inbox-placement testing, provider dashboards, feedback loops, warning signs, and the delisting/recovery workflow.

• Reverse DNS in IPv6 (RFC 8501) and Email

  Why per-address PTR provisioning breaks at IPv6 scale, the five approaches RFC 8501 enumerates (with trade-offs), and what mail receivers expect from IPv6 reverse DNS.

• Sending Email over IPv6

  Why receivers impose stricter rules on IPv6 mail — M3AAWG's 2014 inbound-policy paper (/64 aggregation, reject-without-PTR, reject-without-authentication) and what that means for senders and ESPs today.

• Sending Infrastructure Practices

  Dedicated vs. shared IPs, subdomain strategy, domain warm-up, From-address hygiene, feedback-loop wiring, reputation monitoring tools, and a troubleshooting framework.

• Tracking and Measurement Distortion

  How open and click tracking work mechanically, and how Apple MPP, Microsoft Safe Links, gateway scanners, and image proxies distort the resulting metrics — with guidance on which signals remain trustworthy.