The Infrabox blog · 6 articles

Field notes on deliverability and outbound infrastructure

Authentication, warmup, fleet sizing, and how to read the signals your sending domains give off, written by the engineers and strategists who run them.

Featured

DeliverabilityJan 14, 20269 min read

The Pre-Send Checklist Every Cold Email Domain Needs

Authentication, domain age, warmup ramp, list hygiene, content signals and monitoring: the full checklist to run before a new domain sends its first message.

Priya RamanDeliverability Lead

Read article

Latest articles

Filter by topic, or browse everything we've written.

Deliverability10 min read

SPF, DKIM and DMARC: What Each Record Actually Does

How authentication actually works under the hood: what each record checks, how they chain together through alignment, and where real configurations break.

Jonah ReyesJan 28, 2026

Infrastructure8 min read

How Many Mailboxes Should Actually Live on One Domain

The math behind fleet sizing: daily send caps, blast radius, and a worked formula for going from a monthly send target to a domain and mailbox count.

Marcus OkaforFeb 6, 2026

Playbooks8 min read

Warming a New Sending Domain: The Six-Week Playbook

A week-by-week ramp for building domain reputation from zero, the metrics to watch daily, and the specific thresholds that mean you should pull back.

Elena VasquezFeb 18, 2026

Deliverability8 min read

How to Actually Read a Bounce Message

SMTP reply codes decoded: the difference between a soft and hard bounce, what the enhanced status codes mean, and what to do with each type.

Tobias LinMar 2, 2026

Infrastructure9 min read

Building Outbound Infrastructure That Actually Scales

An architecture-level look at isolation, redundancy, monitoring and rotation: the four principles that separate a fleet that scales from one that eventually collapses.

Diego FontaineMar 16, 2026

Newsletter

Deliverability notes, twice a month

Teardowns of real placement drops, DNS changes worth knowing about, and what we shipped. No fluff, unsubscribe in one click.