[Rilgamon]

local postmaster = {
    ['Der Postmeister'] = true,
    ['The Postmaster'] = true,
}
local f=CreateFrame("Frame")
f:SetScript("OnEvent", function(self,event)
    for i=GetInboxNumItems(),1,-1 do
        local packageIcon, stationeryIcon, sender, subject, money, CODAmount, daysLeft, hasItem, wasRead, wasReturned, textCreated, canReply, isGM =GetInboxHeaderInfo(i)
        if(postmaster[sender]) then
            if(money and money >0) then
                TakeInboxMoney(i)
            end
            if(hasItem) then
                for j = 1, ATTACHMENTS_MAX_RECEIVE do
                    local name, texture, count, quality, canUse = GetInboxItem(i, j)
                    if(name) then
                        TakeInboxItem(i,j)
                    end
                end
            end
            C_Timer.After(5, function() DeleteInboxItem(i) end)
        end
    end
end
f:RegisterEvent("MAIL_INBOX_UPDATE")

You can alter the timer to fit your latency. Not sure if it would work to delete it without the delay.

C_Timer.After(5, function() DeleteInboxItem(i) end)