The most common and most likely answer to this crossword clue is the 10 letter word DELIVERING
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Buddy explains!

The straight part
We know that "posting" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case posting = delivering.The cryptic/wordplay part
In cryptic crossword there's often an wordplay/cryptic part as well.This part involves a more complex hint, such as an anagram, homophone, hidden word, etc.
Sadly, We don't have an explanation for this specific crossword clue yet.
What does DELIVERING mean?
DELIVERING verb- To set free from restraint or danger.
- (process) To do with birth.
- To free from or disburden of anything.
- To bring or transport something to its destination.
- To hand over or surrender (someone or something) to another.
- To produce what was expected or required.
- To express in words or vocalizations, declare, utter, or vocalize.
- To give forth in action or exercise; to discharge.
- To discover; to show.
- To admit; to allow to pass.
- To administer a drug.
- An act of delivering.