Why your emails land in spam (and how to fix it)

A transactional email in spam is a customer who never gets their invoice or can't reset their password. Here are the 8 real causes, from highest to lowest impact.

1. Missing authentication (DKIM/SPF/DMARC)

By far the number one cause. Without these records, Gmail and Outlook don't even bother looking at the content. Read the DKIM, SPF and DMARC guide and make sure all three say PASS.

2. Low IP or domain reputation

New or shared IPs with no history are suspicious. If you are just starting, warm up your sending: raise volume gradually instead of blasting 10,000 emails on day one. A good provider handles this for you.

3. Unmanaged bounces and complaints

Continuing to send to addresses that bounce, or to people who marked you as spam, wrecks your reputation. You need automatic suppression so those addresses block themselves. Zend24 does this by default via SES bounce notifications.

4. Sending transactional and marketing on the same route

If your newsletter generates complaints, it drags your password-reset emails into spam too. Separate the two streams (different subdomains or providers).

5. A From that isn't your domain

Using you@gmail.com as the sender through a service never aligns DMARC. Always send from something@yourdomain.com with a verified domain.

6. Sloppy HTML

Huge images with no text, a single giant link, too many capitals or spammy words in the subject. Keep a healthy text-to-image ratio and write clear, honest subjects.

7. No plain-text version

HTML-only emails score worse. Always include a plain-text alternative (text) alongside the HTML.

8. No List-Unsubscribe

For recurring mail, the one-click unsubscribe header is now required for large senders. Make unsubscribing easy: an unsubscribe beats a spam complaint.

How to measure it

Watch two numbers: your bounce rate (keep it under 2–3%) and your complaint rate (under 0.1%). If they spike, stop and fix before sending more.

Zend24 gives you automatic DKIM, bounce suppression, delivery webhooks and real-time metrics so your emails arrive. Start free with 3,000 emails per month.