Collection
Deliverability & authentication
SPF, DKIM, DMARC, warmup and inbox placement
The unglamorous infrastructure that decides whether anyone reads your copy. Records, ramps, blocklists and the Gmail rules — explained without the XML degree.
27 resources in this collection
Start with these
Domain Health Checker
SPF, DKIM, DMARC and MX in one pass before you send a single email.
Read moreGmail & Outlook sender rules
SPF, DKIM, DMARC and the 0.3% complaint line — for busy people.
Read moreHow email warmup actually works
Pools, domain-safe cohorts, relationship memory, capacity gates and the limits of every inbox claim.
Read moreSPF Record Generator
Build a lean v=spf1 record with the DNS lookup budget counted live.
Read moreEverything else
All deliverability tools
26 free checkers, generators and calculators — no sign-up.
Read moreBlocklist Checker
Sweep your domain's IPs across 13 live DNSBLs with ASN context.
Read moreDKIM, explained: selectors, key sizes and the failures nobody notices
How DKIM signing actually works, what a selector is, why 1024-bit keys are on borrowed time, and how to check the key your domain is really using.
Read moreDMARC monitoring (product)
Aggregate reports turned into daily plain-language answers — included in every plan.
Read moreDMARC Record Generator
Policy ladder, reporting addresses and every tag explained.
Read moreDMARC Report Viewer
Open RUA XML and read who sends as your domain — as a table.
Read moreEmail blacklists: how to check if you're listed — and actually get off
Which DNS blocklists matter in 2026, how to check your domain and IPs in one sweep, and the delisting process that works (it's free, despite what some sites imply).
Read moreEmail Header Analyzer
SPF/DKIM/DMARC verdicts and every hop with per-server delay.
Read moreEmail warmup (product)
Unlimited mailboxes, included free — wired to your reputation guard.
Read moreEmail Warmup Calculator
Day-by-day ramp schedule for new mailboxes, with honest safety warnings.
Read moreEmail warmup week one: the ramp, the safety gates, and what the numbers do not prove
Norbelys starts with a base target of 5 and adds 2 per ramp day, but actual warmup volume can be lower. Here is why capacity, cohorts, health, and provider guidance matter more than a perfect chart.
Read moreHalf of your email opens are robots. Here's how to find the real number.
Apple Mail opens your email automatically, Gmail caches every image, and security software clicks every link. What's actually left when you filter the noise out — and how to make decisions on it.
Read moreHow long does domain warmup take?
Two weeks is a minimum observation period; new or high-volume domains can need four to eight.
Read moreHow to read a DMARC report (no XML degree required)
Gmail, Microsoft and Yahoo send you gzipped XML about every email claiming to be your domain. Here are the four fields that matter and how to spot a spoofer.
Read moreHow to read email headers like a postmaster
Received chains read bottom-to-top, Authentication-Results don't lie, and a five-minute header read explains most delivery mysteries. A field guide.
Read morep=none vs p=quarantine vs p=reject: when to move (and when not to)
More than half of domains with DMARC never leave p=none. Here's the honest ladder from monitoring to enforcement, with the checks to pass before each step.
Read moreSecondary domains for cold email: never send cold from your main domain
The standard 2026 setup: lookalike secondary domains for outbound, 2–3 mailboxes each, round-robin rotation under 40 sends a day — with the DNS records, warmup timeline and redirect details most guides skip.
Read moreSPF records, explained with real examples (and the 10-lookup trap)
What an SPF record actually says, how to read every mechanism, copy-paste examples for common stacks — and the DNS lookup limit that silently voids it.
Read moreThe 0.3% line: how spam complaints decide your sender reputation
Since February 2024, Gmail and Yahoo enforce a hard 0.3% spam-complaint ceiling and want you under 0.1%. Here's the real math — 30 complaints per 10,000 emails — how fast one bad send moves the needle, and how to stay well below it.
Read moreThe blog
Full archive — deliverability, strategy and outreach craft.
Read moreThe pre-send cold email checklist: four gates, sixteen checks
Run every campaign through four gates before it sends — domain, list, copy, send settings. Sixteen checks, each with the free tool or the number that verifies it, printable in your head.
Read moreWhy your emails go to spam (it's rarely the words)
Spam placement in 2026 is mostly reputation, authentication and engagement — not trigger words. A diagnostic order that finds your real problem in 20 minutes.
Read moreYour email list rots before you send: clean it or pay in reputation
Why stale B2B lists turn into bounces, role inboxes, burners and risky domains, how to clean a CSV before launch, and why Norbelys verifies every import instead of selling credit packs.
Read moreReady to put this into practice?
Connect a mailbox and run the same checks on your own domain.