Email & SMTP · 1 min read
Spam Filter Blocks: Improve Content and Sender Reputation
What's happening
Recipient servers or spam filters flagged your emails as spam-like or unsolicited. Bounce messages look like:
- "The message was blocked because it was detected as spam"
- "Rejected because it was flagged as spam or failed content filtering"
- "Recipient previously marked your emails as spam"
Common causes
- Sending to contacts who didn't opt in, or to old or purchased lists
- High complaint rates
- Spammy wording, all caps, lots of exclamation marks or misleading subject lines
- Image-only emails, or too many links
- Links to domains with a poor reputation or link shorteners
- Sudden spikes in volume
Fix it
- Clean your list. Remove unengaged contacts (no opens or clicks in 90+ days), hard bounces and anyone who complained.
- Review content. Write a clear subject line, balance text and images, and limit links to trusted domains.
- Make unsubscribing easy. Keep a visible unsubscribe link in every marketing email.
- Authenticate your domain with SPF, DKIM and DMARC.
- Send to engaged contacts first, then increase volume gradually.
Keep it healthy
- Keep spam complaints below 0.1%.
- Use confirmed opt-in on sign-up forms.
- Send consistently rather than in large bursts.