Domain records#
- SPF: list the servers you send from, in a single SPF record
- DKIM: switch on signing with your email provider
- DMARC: start at p=none, read the reports, then tighten the policy
Volume and warm-up#
Sending hundreds of emails in one go from a new or long-unused mailbox is the quickest way into the spam folder. Build daily volume up gradually, leave random gaps between emails and send during the recipient's working hours.
Content#
- No attachments and few links in a first email
- Plain text rather than templates heavy on images and HTML
- No hard-sell language and no words in capitals
- A subject line that matches what the email is about
List hygiene#
Take bounced addresses off your list for good, and never email anyone again once they've opted out. High bounce and complaint rates damage your domain's reputation quickly.
Diagnose a spam problem#
| Symptom | Likely cause | First thing to check |
|---|---|---|
| Everything goes to spam, even to colleagues | Authentication failing | “Show original” in Gmail: do SPF, DKIM and DMARC say PASS? |
| Fine at first, worse after a week | Volume rose too fast | Daily sends per mailbox and the gaps between them |
| Many hard bounces | Old or guessed addresses | Where the list came from and when it was last checked |
| Spam complaints | Poor targeting or no easy opt-out | Who you're writing to and whether the opt-out works |
| Lands in Promotions | Newsletter-style formatting | Images, HTML layout and the number of links |
A rough guide; mailbox providers don't publish their filtering rules in full.
The full checklist#
- One SPF record that includes every service sending for your domain
- DKIM signing switched on with a 2048-bit key where your provider supports it
- A DMARC record, at least p=none, with reports going to an address someone reads
- Daily volume per mailbox raised step by step, with random gaps
- Plain-text first emails, no attachments, at most one link
- Bounces and opt-outs suppressed automatically and permanently
- Spam complaint rate watched in Google Postmaster Tools and kept well under 0.3%
FAQ
Why are my emails going to spam?
Usually because of missing authentication (SPF, DKIM, DMARC), sending too much from a new mailbox, bulk-style content, or a list with many bounces and complaints. Check them in that order.
How do I check whether my email passes SPF, DKIM and DMARC?
Send an email to a Gmail address, open it and choose “Show original”. Each check should say PASS.
What spam complaint rate is too high?
Gmail and Yahoo ask senders to keep the spam rate below 0.3%. For cold email, aim far lower: one complaint in a few hundred emails is already a warning sign.
Do links and images hurt deliverability?
Many links, tracking-heavy links and image-heavy layouts make an email look like bulk mail. A first email with plain text and at most one link is safest.
Sources
- Email sender guidelines · Google
- Sender Requirements & Recommendations · Yahoo
- Set up Postmaster Tools · Google
- RFC 7208: Sender Policy Framework (SPF) · RFC Editor