Email Deliverability: Why Your Email Goes to Spam

Authentication is not optional any more

The major mailbox providers now effectively require authenticated mail from anyone sending in volume. Without it your messages are filtered or rejected before content is even considered.

SPF lists which servers may send as your domain. DKIM signs each message so it can be verified as unaltered. DMARC tells receivers what to do when the first two fail, and reports who is sending as you.

All three are DNS records, all three are usually a copy and paste from your email platform's setup page, and all three take effect within a day. If you do nothing else from this guide, do these.

Use a subdomain for marketing mail

Send marketing from a subdomain rather than your root domain: something like news.yourdomain.com.

Reputation is tracked per sending domain. If a campaign goes badly, a subdomain absorbs the damage and your invoices, contracts and replies keep arriving. Sending everything from one domain means one bad list can take down your ability to do business by email.

The list is usually the real problem

Mailbox providers judge you mostly on how recipients behave. Low opens, no clicks, and deletions without opening all say the same thing: these people did not want this.

• Never send to a purchased or scraped list, which is the single fastest way to be blocked
• Remove hard bounces immediately and after two or three soft bounces
• Suppress anyone who has not opened in six to twelve months, or run one re-engagement attempt then remove them
• Use double opt-in if your signup form attracts bots or typos
• Make unsubscribing one click, because the alternative is a spam complaint that costs you far more

Warming up, and why volume spikes hurt

A new domain sending to fifty thousand people on day one looks exactly like a spammer, because that is what spammers do.

Start small and grow gradually over two to four weeks, sending first to your most engaged recipients so early signals are positive. If you are moving platforms, warm the new one the same way rather than switching everything overnight.

The same applies to frequency. Going from monthly to daily without warning produces complaints even from people who like you.

Content triggers that still matter

Content filtering is less crude than folklore suggests, and a few things genuinely still hurt.

A single image with no text, which is a classic spam pattern. Link shorteners, which hide the destination. Sending from a no-reply address, which suppresses the replies that would otherwise prove you are legitimate. Wildly mismatched subject and body. And a large ratio of links to words.

Writing FREE in capitals is not the problem people think it is. Sending to people who did not ask is.

How to tell where you actually stand

Do not guess from your own inbox, which is unrepresentative because you are a known contact.

Read the DMARC reports once they are flowing. Watch your open rate by provider, since a collapse at one provider and not others is a reputation signal specific to them. Use a seed test to see placement across several providers before a large send.

And watch the complaint rate. Above roughly one in a thousand is a warning; above three in a thousand and providers will act.

If you are already in spam

Stop sending broadly. Fix authentication first. Cut the list to people who have opened in the last three months and send only to them for several weeks, with genuinely useful content and a clear unsubscribe.

Reputation recovers slowly and only through good behaviour over time. There is no reset button, and any service that offers one is selling something that does not exist.