Double opt-in vs single opt-in with real-time verification
Double opt-in gives you proof of consent but loses 20% to 40% of signups; single opt-in grows faster but lets bad addresses in. How real-time verification changes the trade-off.
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Deliverability, explained.
Guides and research on email verification, bounce rates, catch-all domains, disposable addresses, list hygiene and sender reputation. Written by the people who run the engine.