Third-class mail and Unsolicited mail

Third-class mail noun - Mail consisting of printed matter qualifying for reduced postal rates.

Unsolicited mail and third-class mail are semantically related in marketing mail topic. In some cases you can use "Unsolicited mail" instead a noun phrase "Third-class mail".

Third-class mail and unsolicited mail are semantically related in marketing mail topic. You can use "Third-class mail" instead a noun phrase "Unsolicited mail".