This does raise important notes to gun carriers.
1) The decision was by the US District Court of Colorado. This means it currently just applies in Colorado. When appealed, it will go to the US Court of Appeals for the 10th Circuit. If upheld by the 10th, it will apply in Colorado, Wyoming, Utah, New Mexico, Kansas and Oklahoma (only). Only then might it go to the SCOTUS. But if the USPS does not appeal, it will only apply in Colorado.
2) Even at such time as the decision exists in your area, typically the only way Post Offices will know will be if their bureaucratic system tells them. Since many gun owners know that even police are often not up to date on gun laws, this means that the Post Offices will not have a clue.
So if this Post Office regulation is overturned in your area, do not assume they know. So do them a favor and *tell* them of the change. Even if they don’t believe you, they will check up on it.
Think of it as saving some other gun owner(s) hassle from being arrested for having a gun in a Post Office parking area.
Be sure when you tell them that you don’t have a gun in your car, or they could test your assertion by having you arrested.
If the law is illegal, or is no law at all, they use the process to punish.