Blog · Deliverability
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Authentication, warmup, sender rules, blocklists, and the infrastructure that decides whether anyone sees the message.
Deliverability articles
16 articles
Deliverability8 min
How Email Warmup Actually Works: Ramps, Replies, and Safety Controls
Learn how email warmup works, what mailbox providers require, and how Norbelys controls volume, replies, sender health, and campaign capacity.
Deliverability3 min
The 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.
Deliverability4 min
Secondary 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.
Deliverability6 min
Your 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.
Deliverability7 min
Email 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.
Deliverability5 min
The 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.
Deliverability3 min
How 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.
Deliverability3 min
Half 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.
Deliverability3 min
Email 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).
Deliverability3 min
The Gmail & Outlook sender rules, explained like you're busy
SPF, DKIM, DMARC, one-click unsubscribe and the 0.3% spam threshold — what mailbox providers actually require from senders now, in plain language, with a checklist.
Deliverability3 min
Why 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.
Deliverability7 min
How long does it take to warm up a new email domain?
Use two weeks as a minimum observation period for a low-volume mailbox and four to eight weeks for a new or high-volume domain. The real answer depends on target volume, engagement, authentication, and provider feedback.
Deliverability3 min
How 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.
Deliverability3 min
p=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.
Deliverability4 min
DKIM, 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.
Deliverability4 min
SPF 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.