Getting delivered at all

Permission decides whether you may send. Authentication decides whether anybody receives it. These are separate problems and the second one is where most small senders quietly fail, because nothing tells you that your messages went to spam.

The three records, and why they exist

Email was designed without any way to check that a sender is who it claims to be. The three records are patches on that, and together they let a receiving server verify that a message genuinely came from your domain.

1. 01SPF lists which servers are allowed to send mail for your domain. It is a single line in your DNS, and the common failure is listing one provider and then sending from another.
2. 02DKIM signs each message cryptographically, so the receiving server can confirm it was not altered and did come from you. Your email provider generates the key and you publish it.
3. 03DMARC tells receiving servers what to do when the first two fail, and asks them to report back. It also requires that the visible from address aligns with the domain that passed SPF or DKIM, which is what stops somebody passing their own authentication while displaying your name.

All three are DNS records. They cost nothing, they take an afternoon once, and your email provider documents exactly what to put where.

What the large mailbox providers now require

This stopped being optional. Gmail and Yahoo both publish requirements for bulk senders, meaning roughly those sending above five thousand messages a day, and the two sets are close to identical.

• SPF, DKIM and DMARC, all three. DMARC may start at a policy of none, which asks for reporting without changing how failures are treated, but it has to exist.
• The visible from domain must align with the domain that passes SPF or DKIM.
• One-click unsubscribe for marketing messages, implemented with the List-Unsubscribe-Post header alongside List-Unsubscribe. A link in the body alone does not satisfy it.
• Spam complaint rate kept below 0.3 per cent. Google's own guidance recommends staying under 0.1 per cent as the working target, and treats 0.3 as the line.
• Unsubscribe requests honoured quickly, within two days in Yahoo's guidance.

The things that quietly hurt you

• Sending from a free mailbox address. It cannot be authenticated as yours and increasingly will not be delivered at all.
• A brand-new domain sending to thousands on day one. Reputation is built gradually, so increase volume over weeks rather than starting at full size.
• Hiding the unsubscribe. The people who cannot find it press the spam button, which costs you far more.
• Mailing people who have not heard from you in a year. They have forgotten, and forgetting produces complaints.
• Image-only messages with almost no text, which is a pattern filters treat with suspicion.
• Link shorteners, which obscure the destination and are used by everybody filters are trying to catch.

How to know whether it is working

Guessing is the default and there is no need for it. Register your domain with the free postmaster tools the large providers offer: they show your authentication status, your complaint rate and whether you meet the bulk sender requirements, measured on the receiving side rather than yours.

Then send yourself a test to addresses at two or three different providers and look at where it lands and what the headers say about authentication. Five minutes, and it catches the misconfiguration that your own provider's dashboard reports as a successful send.

If you are already going to spam

Recovering is slower than arriving well in the first place, and the order matters because fixing the content of your messages while the authentication is broken changes nothing.

1. 01Fix authentication first and confirm it from the receiving side rather than from your platform's dashboard. Everything else is wasted effort until this passes.
2. 02Stop sending to anybody who has not engaged in a year. They are the main source of the complaints that put you here.
3. 03Reduce volume and send to your most engaged subscribers only, for several weeks. Reputation recovers through mail that gets opened, which means sending less of it to better addresses.
4. 04Remove every inactive address rather than moving it to a list for later. Later is how this happened.
5. 05Then rebuild volume slowly, watching the complaint rate at each step rather than at the end.

Expect weeks rather than days. Sender reputation is built from a history, so there is no action that resets it, and the common mistake is to send a large apology message to the whole list, which is the worst available move.