USPS Jobs with Felony

I have a question regarding the background check. Do they make any exceptions for folks with felonies? I was convicted when I was 17 of 2 separate felonies, one was the theft of a motor vehicle, and the other was assault back in the late 90s; I have not been in any trouble since. The reason I’m asking is I have heard conflicting responses. I’ve heard it depends on the crime and when it took place, I’ve also heard there is zero tolerance for the Feds. I have worked as an insurance agent and a personal banker as they have made acceptions. Any facts on this topic would be highly appreciated. I really appreciate any help you can provide.