Why is your mail going to spam?
And what order to fix things in, so you don't waste the effort.
Short answer
Almost every case of business mail going to spam comes down to one of the six causes below, and five of the six are configuration rather than the content of the message. Check them in this order: authentication first, reputation second, content last. Rewriting your content while authentication is broken is wasted effort.
1. Missing SPF, DKIM or DMARC
This is the most common cause, and the easiest to fix. If your domain doesn't declare who may send on its behalf, and your mail carries no signature, Gmail has no way to tell you apart from someone forging your domain. Since 2024 Gmail and Yahoo require senders to authenticate; missing it means being downgraded outright.
2. The sending address doesn't match the authenticated domain
Mail leaves from some other service (a sales tool, an invoicing system, a website form) carrying your domain as the sender, while your domain has never authorised that service to send for it. To the receiving system, that is exactly what forgery looks like. Every service that sends on your behalf has to be declared.
3. The domain or IP address is too new
A domain bought last week that starts sending in bulk immediately will be treated with suspicion even if every record is correct. Sending reputation is built over time, and by real recipients opening, replying and not pressing "report spam". Ramp your volume up over the first few weeks rather than sending a thousand messages on day one.
4. Recipients report spam, or you send to dead addresses
The spam-complaint rate is the strongest signal you don't control directly. Mailing a purchased list, a list years out of date, or people who never opted in produces both complaints and a lot of bounces from addresses that no longer exist — together they drag the whole domain down, which spills over onto your ordinary day-to-day mail.
5. Still on a blacklist
If anyone has previously sent spam from this domain or IP — including via an infected machine or a compromised mailbox — the address may sit on a public blocklist. Check with a blacklist lookup service; most lists have a removal form, but you have to fix the underlying cause first.
6. Characteristics of the message itself
Last on the list because it decides the least, despite being blamed the most. The things that genuinely matter: a message that is one image with no text, shortened links, executable attachments, a large mismatch between a link's visible text and its real address, and no way to unsubscribe on bulk mail.
Fix them in this order
- Check the SPF/DKIM/DMARC lines under "Show original". If all three aren't PASS, stop and fix that before touching anything else.
- List every system that sends mail carrying your domain, and authorise them all. One left out keeps damaging the shared reputation.
- Clean the recipient list: drop bouncing addresses, drop people who never opted in.
- Check the blacklists and request removal if you're on one.
- Only then revisit the content and layout of the message.
Things that do NOT help
- Rewording subject lines to avoid "spam trigger words". Modern filters don't work from a banned-word list; this advice has been out of date for a long time.
- Asking a few colleagues to click "not spam". That only affects their own mailbox, and doesn't change how your domain is judged.
- Resending until something gets through. Repeated sending looks more like spam behaviour, not less, and makes things worse.