Operations

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

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.

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.

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.

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

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

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.

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.

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.

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.

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.

How to read the Received trace fields of a delivered message: the field syntax, bottom-to-top order, which hops you can trust, computing per-hop delay across time zones, and how Received relates to Authentication-Results.

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.

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.

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.

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.

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

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.