Double Opt-In
Not legally required, frequently platform-required, always evidence-strengthening. Use it when wrong-number risk or list provenance is a concern.
In a double opt-in flow, the form submission triggers a confirmation text — "Reply YES to confirm" — and only the reply activates the subscription. The handset response proves number ownership and intent in a way no web form can.
Legally, the TCPA requires express written consent, not double opt-in. But the gap between law and practice matters: Klaviyo defaults to it, carriers weight confirmed lists favorably, and litigation over wrong-number and recycled-number claims often turns on exactly the proof double opt-in creates.
Costs: a confirmation step loses 10-25% of signups. The compliance calculus favors double opt-in for imported lists, high-volume ecommerce, and any program where number-entry errors create real exposure.
Frequently asked questions
Related glossary terms
An opt-in is a consumer's affirmative agreement to receive SMS from a brand. Marketing texts require the strictest tier — prior express written consent — captured with full disclosure and retained as evidence.
Express written consent is the TCPA standard for marketing SMS — a clear, conspicuous disclosure with a separate, unchecked affirmative opt-in by the consumer, retained as evidence.
Consent proof is the evidentiary record that a recipient explicitly opted in to SMS — typically a timestamped, IP-logged, hash-locked record of what the user saw and when they consented.