IPA: /ʌnˈpoʊstɪd/
KK: /ʌnˈpoʊstɪd/
Not assigned to a specific place or position, often used in a military context, or refers to something that has not been sent or delivered.
The unposted letters were still in the mailbox, waiting to be sent.
Unposted → It is formed from "un-" (meaning not) and "posted" (from the verb "post", which comes from Latin "ponere", meaning to place or set). The word "unposted" means not placed or not set in a particular position or location.
Think of 'not' ('un-') having something 'set' or 'placed' ('posted') — that's why unposted means something that is not set in place.