mailable

from The Collaborative International Dictionary of English v.0.48

Mailable \Mail"a*ble\, a.
   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.]
   [1913 Webster +PJC] mailbag