Cold email deliverability, without the folklore

Deliverability advice is mostly folklore repeated with confidence. The parts that are real are boring, technical and finite — you can do all of them in an afternoon.

Authenticate the domain

• SPF lists which servers may send as your domain. One record, published in DNS.
• DKIM signs each message so the receiver can verify it was not altered.
• DMARC tells receivers what to do when the first two fail, and asks them to report it.

All three are set up once per domain. Without them your mail is treated as unauthenticated, which in 2026 is close to being treated as spam.

Use a domain you can afford to lose

Send cold email from a separate domain, not the one your customers use to reach you. If the reputation of a sending domain suffers, you want the fallout contained to a domain whose only job was sending.

Start slow, stay slow

A brand new mailbox sending forty messages on its first day looks exactly like a compromised account, because that is what compromised accounts do. Start at five a day and climb over a few weeks. There is no prize for reaching volume quickly.

Caps are a feature

A daily limit per mailbox, enforced by refusing rather than queuing, is the simplest protection there is. Spreading across several mailboxes multiplies your ceiling without raising any single one.

What does not matter as much as people say

• Single words like "free" — modern filters weigh whole messages and sender history, not a banned list.
• Perfectly plain text versus one link — one relevant link is not the problem.
• Sending at 9:14 rather than 9:00 — timing affects whether it is read, not whether it arrives.

What matters most

Whether people reply. Every provider weighs engagement heavily, and no amount of technical hygiene rescues a message nobody wants. Relevance is a deliverability feature.