Email deliverability: how to land in the inbox, not spam

1. Prove who you are

Set up SPF, DKIM and DMARC on the domain you send from. They're the first thing every inbox checks, and missing them is the most common reason good email lands in spam.

2. Send only to people who asked

• Use double opt-in on signup forms so every address is real and wanted.
• Never buy or rent lists.
• Remove hard bounces immediately and never mail people who complained or unsubscribed.
• Make unsubscribing one click. People who can't unsubscribe click "spam" instead, which hurts far more.

3. Keep an eye on two numbers

• Bounce rate: keep it under 2%. Above 5% inbox providers start to distrust you.
• Spam complaint rate: keep it under 0.1%. Gmail's hard limit is 0.3%.

4. Grow volume gradually

A new domain sending 50,000 emails on day one looks like a spammer. Start with your most engaged contacts and roughly double your daily volume as long as bounces and complaints stay low. This is called warming up.

5. Write like a person

• Avoid ALL CAPS subjects and piles of exclamation marks.
• Keep a healthy balance of text and images.
• Avoid link shorteners; link to your own domain.
• Keep emails under about 100 KB so Gmail doesn't clip them.
• Send from a name people recognise.

6. Separate transactional and marketing mail

Password resets and receipts should never suffer because a newsletter got complaints. Send them on separate streams, and ideally separate subdomains.