You wrote a good email, sent it to people who genuinely signed up, and half of it landed in spam. Nothing about that feels fair. The good news: deliverability is not black magic. Four factors decide almost everything, and all four are fixable.

1. Authentication: prove you are you

Three DNS records tell inbox providers your email is really from you: SPF (which servers may send for your domain), DKIM (a cryptographic signature on every message), and DMARC (what to do when the first two fail). Since 2024, Gmail and Yahoo simply refuse bulk mail without them.

You don't need to understand the records, you need them present. A good email tool generates them for you and verifies they are set. This is also why sending from your own domain beats a shared address: the reputation those records build belongs to you.

2. Sender reputation: earned, slowly

Inbox providers score every sending domain on its history: bounces, spam complaints, and how people interact with the mail. A brand-new domain has no history, which is why volume must ramp up gradually. Sending 5,000 emails on day one from a fresh domain is the classic self-inflicted spam-folder wound.

3. List quality: who you send to

  • Hard bounces (addresses that don't exist) signal a careless or purchased list. Remove them immediately and automatically.
  • Spam complaints above roughly 0.3% put you on the fast track to the junk folder.
  • Double opt-in keeps typos, bots and the uninterested off your list before they can hurt you. It is the cheapest deliverability insurance there is.

4. Engagement: send things people open

Filters watch what recipients do. Opens, clicks and replies help; deletions without reading and complaints hurt. The practical consequence: a smaller list of people who actually want your emails outperforms a big cold one, both in sales and in inbox placement.

The checklist

  • SPF, DKIM and DMARC set on your own sending domain
  • New domains warmed up gradually, not blasted
  • Hard bounces and unsubscribes suppressed automatically
  • Double opt-in on every signup form
  • One-click unsubscribe in every campaign (required by Gmail and Yahoo)

SendMerlin does all five by default: guided DNS setup on your own domain, automatic warm-up ramping, suppression handling, and a pre-send check that catches problems before your subscribers ever see them.

Frequently asked questions

Why do my emails land in spam even though people signed up?

Usually missing authentication (SPF, DKIM, DMARC) or a sending address on a domain with no reputation. Fix the DNS records first; they matter more than the content of any single email.

Do spam trigger words like FREE still matter?

Far less than people think. Modern filters weigh sender reputation and engagement much more heavily than word lists. One FREE in a subject won't hurt a trusted sender; a spray of them from an unknown domain will.

How long does warming up a new sending domain take?

Two to four weeks of gradually increasing volume is typical. SendMerlin ramps automatically, roughly doubling daily volume while your metrics stay healthy.