airmail stamp
... that the first official airmail stamp issued for an airmail flight was in May 1917 when Poste italiane overprinted their existing special delivery stamps?
... that the first official <b id="mwFeE"><a href="./Airmail_stamp" id="mwFeI" rel="mw:WikiLink" title="Airmail stamp">airmail stamp</a></b> <i id="mwFeM">(pictured)</i> issued for an <a href="./Airmail" id="mwFeQ" rel="mw:WikiLink" title="Airmail">airmail</a> flight was in May 1917 when <a class="mw-redirect" href="./Poste_italiane" id="mwFeU" rel="mw:WikiLink" title="Poste italiane">Poste italiane</a> <a href="./Overprint" id="mwFeY" rel="mw:WikiLink" title="Overprint">overprinted</a> their existing <a class="mw-redirect" href="./Special_delivery_(postal_service)" id="mwFec" rel="mw:WikiLink" title="Special delivery (postal service)">special delivery</a> stamps?