Different jurisdictions have different requirements:
GDPR: Requires explicit consent for EU residents, including a clear affirmative action (e.g., ticking an unchecked box) and detailed records of when and how consent was obtained. CAN-SPAM Act: Requires a visible opt-out mechanism and mandates honoring opt-out requests promptly. CASL: Canada's Anti-Spam Legislation requires express or implied consent and specific information about the sender and purpose.