You can drop off your ballot in a convenient drop box which is available at the main consular entrance of the U.S. Embassy in Jerusalem at 14 David Flusser Street in Arnona, and another one at the main consular entrance at 71 HaYarkon St in Tel Aviv.  The drop box is available from Monday to Thursday between between 8:00 a.m. and 12:30 p.m. and Friday between 8:00am and 12:00pm, except on local and federal holidays.  No appointment is necessary.