Most labels want no mastering done to the tracks. It means they want your final mix at a normalised level of -3db. If you are using master effects to get a certain sound, then it may be a good idea to send them a version that you have done with this on to say that is how you kinda like it sounding. But its usually better to get a fresh set of ears from a good mastering engineer to get your mix sounding as good as possible. Mastering engineers hate compressed/limited tracks to work with as it leaves them very little room to play with.