Why your email goes to spam: a diagnostic path

Receivers score mail on many signals. Work through them in this order; most problems are in the first two.

1. Authentication

Run the Mail facet on your domain. You want SPF passing with -all, a DKIM signature that aligns with your From domain, and DMARC at least published. A "spoofable" verdict means receivers have no way to distinguish you from an impostor, and they score accordingly. Fix guides: SPF-MISSING, DKIM-NOT-DISCOVERED, DMARC-MISSING.

2. Reputation

Run the blocklist scan on your sending addresses. A listing on Spamhaus or SpamCop explains sudden rejections; UCEPROTECT level 3 listings cover whole networks and are usually noise. Fix the cause before requesting delisting.

3. Infrastructure

• Reverse DNS on the sending address must exist and confirm forward (IP-NO-PTR, IP-PTR-NOT-CONFIRMED).
• The HELO name should match the reverse DNS.
• STARTTLS should be offered with a valid certificate.
• A shared hosting IP carries its neighbours' reputation; a dedicated address or a reputable relay is often the fix.

4. Volume and behaviour

Sudden spikes from a new address are throttled. Warm up gradually. High bounce and complaint rates poison a domain's reputation for weeks; clean lists and honour unsubscribes within seconds.

5. Content

Only after the above. Avoid link shorteners, image-only messages, mismatched link text, and attachments from unknown senders. Include a plain-text part.

6. Read the headers

When a message lands in spam, open it and paste the headers into the header decoder. Authentication-Results tells you what the receiver actually concluded, which beats guessing.