Deliverability: SPF, DKIM and DMARC in practice

If your messages land in spam, in most cases it is not the copy. It is that your domain cannot prove it is the one sending.

The three records and what they do

All three are DNS records, free, and set up in half an hour.

The most common fault

A domain may have exactly one SPF record. In practice you often find two or three, because a new one was added for each new service: one for the mail server, one for the newsletter tool, one for the accounting system.

With multiple SPF records the check fails, and it fails for all of them. The fix is a single record listing every sender in one line.

A second trap: SPF permits at most ten lookups. Include six services and you pass that limit quickly, and the check fails silently.

Introduce DMARC in stages

DMARC tells mailbox providers what to do with messages that fail the check. Introduce it in three stages or you will accidentally block your own systems.

1. Policy none, four weeks. Nothing is rejected, you only receive reports. Evaluate them and find every system sending in your name.
2. Policy quarantine, four weeks. Failing messages land in spam. Keep watching the reports.
3. Policy reject. Failing messages are rejected. Only now are you protected against abuse of your domain.

Stage one reports routinely surface surprises: the ticketing system, the shop, the booking tool, an old form on a forgotten page.

Separate the sending domain

Use a dedicated subdomain for bulk sending, such as news.yourdomain.com. The reason: domain reputation is assessed separately, so a poor send does not damage the deliverability of your business correspondence.

The more important part: recipient behaviour

Technology is the entry ticket, not the seat. Mailbox providers judge above all how people treat your messages.

Positive: opens, clicks, replies, moving out of spam, adding to the address book. Negative: deleting without opening, marking as spam, undeliverable addresses, long inactivity.

From that follows the single most effective measure: send less often to people who do not respond. A list of 1,000 active addresses is delivered better than one of 10,000 where 800 read.

Warming up a new domain

A fresh sending domain has no reputation. Send 20,000 messages at once and you will be blocked. Ramp up over two to three weeks: day one around 200, then increase by 50 per cent daily, starting with the most active addresses. That order generates positive signals from the outset.