CAN-SPAM in the United States
CAN-SPAM allows unsolicited commercial email but sets conditions. Headers and subject lines must not mislead, the message must include the sender's valid physical postal address, and every message needs a clear way to opt out that works for at least 30 days after sending. Opt-outs must be honoured within 10 business days, and the sender stays responsible even when a tool or an agency sends on its behalf.