Gmail blocks 99.9% of spam — nearly 15 billion messages daily — using multi-layered ML including LLM-based semantic analysis.
Engagement signals Gmail tracks:
✅ Positive signals:
- Replies (the MOST powerful — 2-3% reply rate > 40% open rate with no replies)
- Opens, clicks, forwards
- Time spent reading
- Moving from Promotions to Primary
- "Not Spam" markings
❌ Negative signals:
- Spam reports (most damaging)
- Deletions without reading
- "Mark as read" without opening
- Ignored/unread emails
⚠️ Since November 2025, Gmail issues permanent 550 rejections for non-compliant bulk senders. No more second chances.
The Promotions tab is NOT spam — emails there still drive significant engagement.
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