The library is open

Everything we publish now sits in one place, at /resources, and none of it is behind a form. This is a note about what is on the shelf, plus one decision we would happily argue about.

What is on the shelf

Five field guides, one for each part of email that decides whether your mail lands: deliverability, business email on your own domain, newsletters, cold outreach, and what the category actually costs. Each guide anchors a cluster of shorter pieces in the journal, which is where the working detail lives. The DNS records. The diagnostics in the order we run them. The specific bounce codes and what each one means.

Dispatches are this format: shipping notes, changes at the mailbox providers, and numbers out of our own system. They go up when something happens, not on a publishing calendar.

Downloads are the checklists we run ourselves, as printable PDFs. Tools is two calculators. The first reads our pricing dataset and tells you what the major providers would charge at your subscriber count and team size. The second prints the warm-up ramp our send path enforces in code, day by day, from whatever date a new domain starts sending.

There is also the glossary: 35 terms in plain English, each with the number attached where a number exists.

Nothing is gated, and here is why

The standard trade is an email address for a PDF. We are not making that trade, and the reason is not generosity.

A list assembled that way fills up with people who wanted one file and never wanted a newsletter. They typed an address to get past a form, and six weeks later a campaign arrives from a name they do not recognize. What they reach for is not the unsubscribe link. It is the spam button, and that is the outcome that costs you something real.

The arithmetic is unkind at small scale. Mailbox providers score complaint rate, and Google's bulk sender rules put delivery mitigation out of reach at 0.3%, with under 0.1% as the number every deliverability team works toward (Google's sender guidelines, February 2024, current as of August 2026). On a list of 2,000 people, six spam-button presses in a single send is 0.3% exactly. Six. A gated checklist can hand you those six in an afternoon.

So we would rather have a smaller list that opens things. That is not a slogan we invented for a landing page, it is the same policy we apply to our own sending: double opt-in at signup, most-engaged recipients first, inactives sunset rather than carried along. Publishing a lead-magnet gate while running that playbook would be incoherent.

The self-interested version, since this is a build-in-public note and the honest framing costs nothing: we sell one thing, a flat-rate workspace at $50 per domain. We would rather be found on the day you need a mailbox than collect addresses from people who needed a PDF. The one form on this site is the waitlist, and that is a different trade, because there you are asking us for something.

The calculators run entirely in your browser. Nothing you type into them is transmitted anywhere, because there is nowhere for it to go.

The dataset, and what it assumes

The comparison tables and the cost calculator read the same file: 14 providers, priced by hand from their live pricing pages, each number carrying the month it was checked. Right now that stamp reads August 2026 across the board.

By hand is the part worth stating. Nothing here was scraped. Someone opened each pricing page, worked out the cheapest plan a real person at that size would actually buy, and recorded what it costs alongside what breaks at that tier. Free tiers are recorded with their limits, including the ones that got smaller this year. The assumptions travel with the numbers: annual billing where a provider offers it, introductory promotions excluded because they expire and the bill after them is the real bill, and contact-tier pricing quoted at the tier boundary instead of averaged into something smooth.

Now the limits, because a methodology without them is an advertisement. Fourteen providers is not the whole market. It is the set our readers compare in practice, weighted toward newsletter platforms and business email, and it leaves out plenty of good tools. Usage-based plans depend on assumptions we picked, and yours will differ. Prices change without announcement and every one of ours starts aging the day it is checked, which is why each carries a date, and why we recheck quarterly and again whenever a page republishes.

If a number is wrong, tell us. The address is hello@letterduck.com, corrections get noted on the page rather than quietly edited in, and pricing errors jump the queue. The rest of the policy, including the plain statement that drafting here is AI-assisted and that a person checks every figure against its source before it ships, is in our editorial standards.

What this is not

No product feature shipped with any of this. LetterDuck is live and in waitlist mode, taking domains in waves, and the library is documentation and reporting rather than a release. We are writing down what we run while we run it, which caps how fast the shelf can grow and is also the only quality guarantee we can honestly make. When the system teaches us something, it gets published. When it does not, nothing does.

Where to start

If your mail is going to spam, open the deliverability handbook and work through the checks in the order they are listed, because the order is the point.

If you are pricing a move off your current platform, open the cost calculator and put in your real subscriber count rather than the round number on the provider's pricing page.

If you only came for the checklist, it is in downloads. Take it. There is no form.