$ man lemlist-wiki/lead-management

Lead Management & Deduplication

Stop emailing the same person from three campaigns. Lemlist handles this if you set it up.

Lemlist deduplicates by email address across your entire workspace. If a lead is already in an active campaign, they won't be added to a second one. This is on by default - don't turn it off.

The edge case: same person, different email. Company email in Campaign A, personal email in Campaign B. Lemlist can't catch this. Your enrichment layer (Clay, Apollo) should dedupe by domain before handoff.