In October 2011, USCIS announced process improvements for particular
naturalization and citizenship forms. Part of this process was to
centralize the intake of Forms N-336, N-600 and N-600K to the Phoenix
Lockbox facility, and Form N-300 to the Dallas Lockbox facility. This
change was implemented to streamline the way that forms are processed by
USCIS and improve the speed and efficiency of the federal agency.
USCIS has just published a reminder: all forms affected by this change
that are received at local and district offices after December 2, 2011,
are now no longer being forwarded to the appropriate USCIS Lockbox
facility for processing. Instead these forms are being returned to the
filer with instructions on how to correctly file the form (and what
Lockbox location to submit it to).