The closest mailbox to the Library Annex is located on Font Blvd. To reach it you must turn left onto Lake Merced Blvd, walk two blocks and turn left onto Font Blvd. The box is about halfway up the block. It does not have pickup times listed but it is regularly picked up.
Two other mailboxes can be found on 19th Avenue. One is in front of HSS and another by the MUNI 29/18 stop in front of Stonestown at 19th Avenue and Buckingham Way.
The closest post office is located in Lakeshore Plaza at 1543 Sloat Blvd.