The purity and precision of postal addresses within a mailing list. The address hygiene is directly correlated with a mail-out's delivery effectiveness, and much more on the direct marketing campaign's efficacy. Poor address hygiene will result in a significantly high proportion of rejected mail because of non-delivery, while a good address hygiene will result in a small proportion of non-delivered mail. The address hygiene is usually better on mailing lists for solicited items, such as magazine or newspaper subscriptions, than on a direct marketers' lists for unsolicited promotional mail.