[Tonyleila]

Thanks for all your recommendations I tryed it with grepWin.
This addon contain SendAddonMessage:
BigWigs, BugSack, Capping, Hermes, PhonixStyle, Pokemon Trainer, Recount
I looked into all of them but did not find anything without INSTANCE_CHAT.

But also PhoenixStyle and RaidSlackCheck have it and I'm not shure about the code
Most things are like

function psmarksoff(where)
local inInstance, instanceType = IsInInstance()
if instanceType~="pvp" then
if where==nil then
  if select(3,GetInstanceInfo())==7 or IsLFGModeActive(LE_LFG_CATEGORY_LFD) then
    SendAddonMessage("PSaddon", "16off", "instance_chat")
  else
    SendAddonMessage("PSaddon", "16off", "raid")
  end
else
SendAddonMessage("PSaddon", "16off", where)
end
end
end

But there are also things like

--BIGWIGS
SendAddonMessage("BigWigs", "T:BWCustomBar "..pstime.." "..pstext, "RAID")
--DXE
SendAddonMessage("DXE", "^1^SAlertsRaidBar^N"..pstime.."^S~`"..pstext.."^^", "RAID")

So maybe someone can look into the addon code of RSC and PS and tell me if its this addon causing the you are not in a party spam. Thanks!