Synonyms and related words :
PP, RD, RFD, airmail, book post, correspondence, direct mail, direct-mail selling, express, fourth-class mail, frank, halfpenny post, junk mail, letter post, letters, mail, mail-order selling, mailing list, newspaper post, post, post day, registered mail, rural delivery, rural free delivery, sea mail, seapost, special delivery, special handling, surface mail