Missouri Revised Statutes Title XXVI. Trade and Commerce § 407.1123. Unsolicited electronic mail without either return email address or toll-free number prohibited

1. No person or entity conducting business in this state shall electronically mail (email) or cause to be emailed documents consisting of advertising material for the lease, sale, rental, gift offer or other disposition of any realty, goods, services or extensions of credit without a toll-free telephone number or valid sender-operated return email address that the recipient of the unsolicited documents may call or email to notify the sender not to email any further unsolicited documents.

2. It is an unlawful merchandising practice pursuant to section 407.020 to assist in the transmission of an unsolicited commercial electronic mail message when the person providing the assistance knows, or consciously avoids knowing, that the initiator of the commercial electronic mail message is engaged, or intends to engage, in any act or practice that violates sections 407.1120 to 407.1132.

3. As used in this section, the phrase “assist or initiate the transmission” does not include or refer to the transmission of any commercial electronic mail message by a telecommunications utility or internet service provider to the extent that the telecommunications utility or internet service provider merely carries such transmission over its network.