Why mail lands in spam

Nobody at Google or Microsoft decided they dislike you. Spam placement is the outcome of a few mechanical checks and one slow-moving judgement about your reputation.

This explains what those are, in the order worth fixing them.

First: authentication. Receiving servers check whether you are allowed to send as your domain — SPF, DKIM and DMARC. A domain missing DKIM is the most common reason a real business's mail lands in spam. This is mechanical, binary, and entirely within your control. Fix it first: DNS without the jargon.

Second: reputation. Receiving servers remember how people treat your mail. Bounces, complaints and deleted-unread all count against you; opens and replies count for you. Reputation is earned slowly and lost quickly, and it attaches to your domain, so a bad campaign hurts your invoices too.

Third: the list. Sending to addresses that do not exist is the fastest way to damage reputation. So is mailing people who never asked. Bought lists are catastrophic — spam traps are addresses that exist only to catch people mailing lists they should not have.

Fourth, and least: content. Yes, all-capitals subject lines and "FREE!!!" hurt. But content is the last thing filters weigh, and rewording an email will not rescue a domain with no DKIM and a ten percent bounce rate. People reach for this first because it is the easiest to change, which is precisely why it disappoints.

One more thing that behaves like all four at once: sudden volume. An address that has never sent, suddenly sending ten thousand messages, looks exactly like a compromised account — because that is usually what it is. Build up gradually.

1. Open Deliverability and fix every domain not showing all three of SPF, DKIM and DMARC. Nothing else matters as much.
2. Get your bounce rate down. Import your existing unsubscribes and bounces into Suppressions before your first campaign.
3. Only mail people who asked. If you cannot say where an address came from, do not use it.
4. Make unsubscribing easy and honour it immediately. Someone who cannot find the unsubscribe link presses the spam button instead, and that costs you far more.
5. If you are starting to send in volume, build up over a couple of weeks rather than starting at full rate.
6. Only then look at your subject lines and content.

One recipient says your mail goes to their spam folder. Check Email logs to confirm it was delivered. If it was, this is their organization's filter, and the reliable fix is them marking it not-spam or allowlisting your address.

Everyone at one company is affected. Their mail system has an opinion about your domain. Authentication first, then ask their IT team what their filter reported — they can see a reason you cannot.

It started suddenly. Something changed: a DNS record edited, a campaign to an old list, or an application sending far more than usual. Check Reports for a volume jump.

Everything is authenticated and it still happens. Then it is reputation, and reputation recovers by sending good mail to people who want it, consistently, for a while. There is no switch for this.

• Deliverability — your own numbers
• Suppressions — protecting your reputation
• DNS without the jargon — the records behind authentication