What is the term for a sales campaign that is conducted through the mail?

The term for a sales campaign that is conducted through the mail is "Direct-response." This term specifically refers to marketing strategies aimed at prompting immediate responses from recipients, typically through mail, by encouraging them to take action such as making a purchase, signing up for a service, or requesting more information. Direct-response marketing is designed to elicit a quick reaction, making it distinct from other marketing approaches that might focus on brand awareness or long-term engagement.

The other options represent different types of marketing or sales activities. Telemarketing involves using the phone to reach potential customers; cold calling is a form of telemarketing where calls are made to individuals who have not previously expressed interest in the product or service. Email marketing utilizes electronic mail to communicate with prospects and customers but does not involve physical mail. Hence, "Direct-response" is the most accurate descriptor for a sales campaign specifically conducted through mail.