Why Your Emails Land in Outlook’s Spam Folder (And How To Fix It)

Outlook and Hotmail use aggressive, proprietary spam filters built on machine learning, not just keyword lists.

These filters analyze:

1. Metadata & Headers:

• Mismatched "Reply-To" and "From" fields

• Missing or misconfigured SPF, DKIM, and DMARC

• Suspicious routing paths or shared IPs flagged by DNSBLs

2. Content Features:

• N-gram language patterns from past spam

• High entropy attachments or uncommon file types

• URL shortening services or blacklisted domains

3. Behavioral Patterns:

• Sudden changes in volume

• High bounce or complaint rates

• Low engagement (no opens or replies)

4. Live Scoring via ML Models:

• Logistic Regression, SVMs, or Transformers classify email in real-time

• Bayesian spam scores combined with user-specific engagement signals

• Thresholds adjust per user; one recipient’s “spam” might be another’s “ham”

Why This Breaks Most ESPs:
Even if you pass authentication, Outlook penalizes senders based on past behavior, IP reputation, and user-level interactions. Shared infrastructure amplifies risk—one bad sender affects all.

How Lemon Email Fixes It:
Lemón isolates your traffic with dedicated IPs optimized for Outlook/Hotmail delivery. We fine-tune infrastructure using:

• AI-powered IP rotation and warm-up

• Pre-tested, Outlook-tolerant header structures

• Clean, responsive HTML frameworks that minimize NLP flags

• Engagement-primed delivery timing and adaptive routing

Lemon Email doesn’t just send email—it navigates spam filters. You write. We deliver. Even to Outlook.

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