# Follow-Up Engine — Operational Troubleshooting

**Document Version:** 1.0.0 (Phase 13)

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## Common Scenarios & Resolutions

### 1. Follow-Up Remains in "Due" State
- **Cause:** No sales rep marked it completed, or mail sending was disabled.
- **Resolution:** Click **[Mark Done]** in the Follow-Up center or Lead Detail card.

### 2. Follow-Up Shows "Failed"
- **Cause:** Transient SMTP network error or invalid recipient email.
- **Resolution:** Inspect failure reason in follow-up details. The system automatically retries with exponential backoff up to 3 attempts.

### 3. Duplicate Follow-Up Protection
- **Cause:** Attempting to enroll the same lead into an already active sequence.
- **Resolution:** A lead can only have one active enrollment per sequence. If needed, cancel the current enrollment before enrolling into a new sequence.