You can write the best newsletter in your industry and still reach nobody. Deliverability is decided before a single reader opens anything: by your domain's reputation, by the authentication records on your DNS, and by how hundreds of recipients behaved with your last three emails.

The good news is that most deliverability failures are boring and fixable. Here are the ones that account for the majority of "our emails went to spam" complaints, in the order worth checking.

1. Authentication: SPF, DKIM and DMARC

These three DNS records tell receiving servers that you really sent the message. Without them, your mail is treated as unverified — which is fine until a spammer fakes your address and reputation collapses.

  • SPF lists the servers allowed to send on your behalf. One record per domain, and it must include your email tool's sending domain.
  • DKIM adds a cryptographic signature that survives forwarding. Most tools give you a CNAME or TXT record to paste.
  • DMARC tells the receiver what to do when a message fails the first two checks. Start with p=none and a reporting address, watch the reports for a fortnight, then move to p=quarantine.

If you send marketing email through one tool and invoices through another, every tool needs its own authorisation. A missing record for the tool you use once a month is the classic cause of a sudden spam-foldering.

2. Send from a subdomain you control

Send marketing from mail.yourdomain.com rather than the bare domain. Transactional mail — receipts, password resets, delivery notices — should keep the root domain clean. That way a badly received campaign cannot damage the deliverability of the emails your business actually depends on.

3. List hygiene beats clever copy

Engagement is the strongest signal receiving servers have. A list that ignores you for a year is a liability, not an asset.

  • Remove hard bounces immediately and never re-import them.
  • Suppress anyone who has not opened or clicked in nine to twelve months, before they mark you as spam.
  • Use double opt-in if your signup form is on a page with high bot traffic.
  • Never buy a list. Not once, not "just to test".

It feels like throwing away audience. In practice, a smaller list that opens regularly lands in the inbox, which is worth more than a large list that does not.

4. Send consistently, not in bursts

Reputation is built by predictable volume. A new domain that sends 5,000 emails on day one looks exactly like a spam operation. If you are starting out, begin with the most engaged segment, send in small batches for the first two weeks, and double volume gradually.

The same applies after a long silence. Coming back from eight months of nothing with a hard-sell campaign is the fastest way to collect complaints.

5. Make unsubscribing easy

One-click unsubscribe is required for bulk senders by the major providers, and it protects you. A visible unsubscribe link reduces spam complaints, and complaints cost far more than a lost subscriber. Put the link in the footer, keep the process to one click, and honour it within 24 hours.

6. Keep the HTML sane

A few technical habits prevent avoidable filtering:

  • Keep the message under 100 KB; heavy images with little text look like advertising.
  • Use one clear text link to your site rather than ten tracked redirects.
  • Avoid image-only emails — include real text so filters can read the message.
  • Host images on your own domain, not a shared CDN full of unknown senders.
  • Test rendering before sending; broken HTML increases complaints.

7. Read the reports you already have

Most email tools show bounces, complaints and placement by provider. Look for patterns rather than single events: Gmail spam-foldering while Outlook is fine usually points to authentication or engagement; everything failing at once usually points to a blocklist or a broken DNS record.

Check your sending domain against a reputation service before a big campaign, not after. Two minutes of checking saves a week of apologising.

8. When it is already broken

  1. Pause campaigns. Keep sending transactional mail only.
  2. Verify all three records with a DNS checker, including the subdomain you send from.
  3. Check blocklists and request removal where you have a legitimate case.
  4. Send a plain-text, low-link email to your most engaged 10% and watch what happens.
  5. Rebuild volume slowly over two to three weeks before resuming a normal schedule.

Checklist

  • SPF, DKIM and DMARC present and passing for every tool you send from
  • Marketing on a subdomain, transactional mail on the root
  • Bounces removed, inactive subscribers suppressed
  • Volume ramped gradually, sends consistent week to week
  • One-click unsubscribe in place and honoured
  • Message under 100 KB with real text, not one big image
  • Reputation checked before campaigns, not after

Deliverability is the plumbing under the newsletter itself and under the subject line. Fix the pipes first; the writing only works if the message arrives.