Mailing need (5)
I believe the answer is:
stamp
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">mailing need</span>' is the definition.<br/ ><span class="explanation-format__explanation">(I've seen this in another clue)</span><br/ ><br/ >This is all the clue.<br/ ></span>
(Other definitions for stamp that I've seen before include "Postage paid label" , "contributions?" , "Tread heavily (on an envelope?)" , "Impress with a mark" , "Seal" .)