When using rcon, editing mapedits files, writing scripts, or in several other situations
You need to use server commands.. these are used just like regular admin commands

Complete list of server commands added by twifire:
entitylist - shows all ents in map
mapeditsexec <mapfile> - execs the given mapfile, auto-compensating for a change in mc_editfolder cvar
addeffectrcon <fx> <x> <y> <z> <yaw> <pitch> <roll> - similar to ammap_addeffect
addmodelrcon3 <model> <x> <y> <z> <yaw> <pitch> roll> - similar to ammap_addmodel
addghoulrcon <model> <x> <y> <z> <yaw> <pitch> <roll> - similar to ammap_addglm
addanyent <classname> <x> <y> <z> <spawnstring> - similar to ammap_place
mcaddtele <telename> <x> <y> <z> <yaw> - similar to amteles add
mcmap_setvar <entnum> <variable> <value> - similar to ammap_setvar
mcmap_respawn <entnum> - similar to ammap_respawn
mcmap_usetarget <targetname> - similar to ammap_usetarget
mcmap_delent <entnum> - similar to ammap_delent
mcmap_save <entnum> - similar to ammap_save
mcmap_setangles <ent> <yaw> <pitch> <roll> - similar to ammap_setangles
mcmap_nudgeent <ent> <x> <y> <z> - similar to ammap_nudgeent
addmcsentry <group> <x> <y> <z> - spawns a group sentry
addmcshield <group> <x> <y> <z> <yaw> - spawns a group shield
addlightrcon <x> <y> <z> <r> <g> <b> <power> - similar to ammap_addlight
cshaderrcon <shaderold> <shadernew> - similar to amshader
mctele <player> <x> <y> <z> - similar to amtele
rmap <map> - change the map without worrying mc_crash_fix
mckick <player> - similar to amkick
rstatus - similar to amstatus
rtestfile <filename> - check if a file exists
mcjetpack_effect <fx> - change the jetpack effect
say2 <message> - similar to amannounce all
mckill <player> - similar to amkill
waterworld - make everyone drown.
statuswrite - Write server status info in HTML to a file.
nomapfix - temporarily disable the effects of mc_safemap
specialgametype <gt> - similar to amspecialgametype

say <message> is now the only way to chat from server, to prevent accidentally announcing passwords