Mailable adj. Admissible lawfully into the mail. Opposed to non-mailable. Dangerous items such as explosives, weapons, or corrosive chemicals are often classified by the postal authorities as non-mailable. (U.S.)
... especially for learners. Showing the Exact Location of all the Organs of the Brain. Price, including box for packing, $1 25. [By Express. Not mailable.] ... — Vegetable Diet: As Sanctioned by Medical Men, and by Experience in All Ages • William Andrus Alcott
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