That can be (physically and/or legally) sent by mail.(adjective)
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Use "mailable" in a sentence
"Republicans like mailable micro-minds that they can mold to their agenda."
"OK I was hoping for some Twlight E-mailable/downloadable valentines to send some friends but I guess I am going to have to make my own."
"I've seen technology that would certainly beef up MoMA snaps: Stickybits, for instance, uses scanned bar codes that allow users to attach video, photos, and other digital information to birthday cards, mailable objects, and any other scannable item: even walls and lamp posts."