A new domain cannot reach an inbox yet.

It measures, it does not estimate

Most warm-up tools tell you a message was delivered. Delivered is not the same as read, and it is certainly not the same as inbox. Firkin holds credentials to the mailbox on the other side, so after every message it opens that mailbox and looks at which folder the message is actually sitting in.

It also reads the verdict the receiving provider stamped on the message itself. Gmail and Microsoft both record whether your SPF, DKIM and DMARC checks passed on arrival. Your DNS records parsing correctly is one question. Gmail agreeing that the signature on a real message is valid is a different one, and only the second predicts anything.

The number nobody else shows you

Here is the uncomfortable part of every warm-up report you have ever read. That inbox rate was measured against mailboxes that write back to you, and an established correspondence is most of what a spam filter weighs. So the figure is flattered, and the cold campaign it is supposed to predict looks nothing like it.

Firkin reports both. Placement with the mailboxes that reply, and placement with mailboxes that only ever receive and never answer, which is the closest thing to what a real prospect sees. The gap between those two is the part of your inbox rate that the relationship is buying, and it is usually several points. The lower number is the honest one.

Who your mail goes to

Mailboxes being warmed exchange mail with each other. Yours writes to other people's and answers theirs, which is what makes the pattern look like correspondence instead of a broadcast. You connect the mailbox you want warmed and nothing else.

The fair criticism of any shared network is that you cannot choose your company, and a pool full of burner domains drags everyone in it down. Firkin matches mailboxes within a band of each other rather than pairing a new domain with whatever is available, tracks what each one contributes against what it takes, and will not pool a mailbox on a domain you have not proven you control. Addresses stay private. You see how many mailboxes are available to exchange with, never who they belong to.

What it will not tell you

There is no reputation score, because there is no such thing per domain. Google publishes one in Postmaster Tools, and it needs far more daily volume than a warm-up produces before it reports anything at all. Every other score on the market rates the sending IP, which for most people belongs to Google or Microsoft and is shared with thousands of strangers. A number like that on your dashboard would look authoritative and describe someone else.

So Firkin shows four measured facts and no invented composite: where receivers filed your mail, what they concluded about your authentication, which providers have actually judged you, and whether the domain is on a blocklist. Every rate carries the count it was measured over, because a perfect score from three messages is not a record.

Why the name

A firkin is a small cask. Good things are not rushed.