Simple lua output script I use in QA

smtp-output.lua

function init (args)
    local needs = {}
    needs["protocol"] = "smtp"
    return needs
end

function setup (args)
    smtp = 0
    filename = SCLogPath() .. "/smtp-lua.log"
    SCLogInfo(filename);
end

function log(args)
    ts = SCPacketTimeString()
    ipver, srcip, dstip, proto, sp, dp = SCFlowTuple()

    file = assert(io.open(filename, "w"))

    local a = SMTPGetMailFrom()
    if (a) then
        print(a)
    end
    local b = SMTPGetMimeField("x-mailer")
    if(b) then
        print(b)
    end
    local c = {}
    c = SMTPGetRcptList()
    for i, v in pairs(c) do
        print(i, v)
    end
    local d = { }
    d = SMTPGetMimeList()
    for i, v in pairs(d) do
        local e = SMTPGetMimeField(v)
        print(i, v, e)
    end

    file:write ("SMTP::" .. a .. "::" .. b .. "::SMTP")

    file:write("\n")
    file:flush()
    file.close(file)
    smtp = smtp + 1
end

function deinit (args)
    print ("SMTP transactions logged: " .. smtp);
end