Email deliverability has changed. What worked two years ago no longer guarantees inbox placement. Gmail and Yahoo have tightened bulk sender requirements, and they are far less tolerant of weak authentication, poor list hygiene or erratic sending behaviour.
If your campaigns are landing in spam, it’s rarely random. There is almost always a technical or behavioural reason behind it. This guide breaks down what actually moves the needle in inbox placement and what tends to damage it.
1. The Non-Negotiable Technical Setup (Authentication)
If you do not have these three protocols set up, your emails are almost guaranteed to be flagged as spam. They verify your identity and prevent spoofing.
- SPF (Sender Policy Framework): A DNS record that lists the IP addresses authorised to send emails on behalf of your domain.
- DKIM (DomainKeys Identified Mail): Adds a digital signature to your emails, proving they were sent from your domain and haven’t been tampered with in transit.
- DMARC (Domain-based Message Authentication, Reporting, and Conformance): Tells receiving servers what to do if an email fails SPF or DKIM checks (e.g., reject it or send it to spam).
2. List Hygiene and Consent
Sending emails to people who don’t want them destroys your sender reputation faster than anything else.
Clean Your List Regularly: Immediately remove “hard bounces” (invalid email addresses). Segment out inactive subscribers who haven’t opened an email in 3–6 months and either run a re-engagement campaign or remove them entirely.
Use Double Opt-In: When a user subscribes, send an automated email asking them to click a link to confirm. This ensures the email address is valid, and the user genuinely wants your content.
Make Unsubscribing Effortless: Include a highly visible, one-click unsubscribe link in every email. If people can’t find the unsubscribe link, they will hit the “Mark as Spam” button instead, which severely damages your reputation.
3. Sender Reputation and Behaviour
Email providers track your behaviour over time. A good reputation means a direct ticket to the inbox.
- Warm Up Your IP/Domain: If you are using a new domain or IP address, do not send 10,000 emails on day one. Start by sending a small number of emails to highly engaged users, gradually increasing the volume over several weeks.
- Maintain a Consistent Volume: Avoid erratic sending patterns. Sending 100 emails one week and 50,000 the next looks highly suspicious to spam filters.
- Monitor Postmaster Tools: Sign up for Google Postmaster Tools and Microsoft SNDS (Smart Network Data Services). These free tools show you exactly how these providers view your domain’s reputation and will alert you to spam spikes.
4. Content and Formatting Rules
Spam filters scan the actual contents of your email to look for red flags.
- Avoid “Spammy” Language: Limit the use of all-caps, excessive exclamation points, and trigger words (e.g., “FREE!!!”, “Earn $$”, “Urgent”, “Guaranteed”).
- Balance Text and Images: Emails that are just one giant image are immediately flagged by spam filters because they can’t read the text. Aim for a ratio of at least 60% text to 40% images.
- Don’t Use Link Shorteners: Services like Bitly are heavily abused by spammers to hide malicious URLs. Always use full links or hyperlink your text directly.
- Include a Physical Address: To comply with anti-spam laws such as CAN-SPAM (US) and GDPR (Europe), you must include your business’s physical mailing address in the email footer.
If you’d like, we can guide you through checking whether your domain has SPF, DKIM, and DMARC correctly configured and whether they’re properly aligned.
And if you’re facing wider email performance issues (particularly for e-commerce, SaaS or high-volume publishers), that’s something we regularly help businesses diagnose and stabilise.
