Per https://www.campaignmonitor.com/blog/email-marketing/39-of-senders-use-confirmed-opt-in-lists-do-you/ https://www.campaignmonitor.com/blog/email-marketing/3

Per https://www.campaignmonitor.com/blog/email-marketing/39-of-senders-use-confirmed-opt-in-lists-do-you/ https://www.campaignmonitor.com/blog/email-marketing/39-of-s... double-opt-in is a best practice but not strictly required. (IANAL and local laws may vary.)