Spam Score
A numerical rating that predicts how likely an email is to be classified as spam by ISP filters.
Spam score is a numerical rating assigned to an email by content filters and anti-spam systems like SpamAssassin, Barracuda, and proprietary ISP filters. The score is based on dozens of factors in the email's content, headers, and sending infrastructure. If the score exceeds a threshold (typically 5.0 on SpamAssassin's scale), the email is flagged as spam.
Factors that increase spam score:
- Content triggers: ALL CAPS, excessive exclamation marks, spammy phrases ("Act now!", "Free money", "Click here")
- Technical issues: Missing SPF/DKIM/DMARC authentication, suspicious headers, mismatched From/Reply-To domains
- HTML problems: High image-to-text ratio, broken HTML, hidden text, URL shorteners
- Sending behavior: New IP/domain with no reputation, sudden volume spikes, high bounce rates
- List quality: Sending to spam traps, invalid addresses, or unengaged recipients
How to minimize spam score: Write naturally, authenticate your domain properly, maintain clean lists, and test your emails before sending. Tools like mail-tester.com and GlockApps can analyze your spam score before you send. SendSure's Deliverability Testing tool evaluates your domain's authentication and infrastructure factors that contribute to spam scoring.
Related Terms
Sender Reputation
A score assigned by ISPs to your email sending domain/IP that determines whether your emails reach the inbox.
Email Blacklist (RBL)
A database of IP addresses and domains known to send spam, used by ISPs to filter incoming email.
Email Authentication
The umbrella term for protocols (SPF, DKIM, DMARC) that verify a sender's identity and prevent email spoofing.
Inbox Placement Rate
The percentage of sent emails that successfully land in the recipient's primary inbox rather than spam, promotions, or junk folders.
Want to learn more?
Read our in-depth blog posts on email verification and deliverability.