Yes it is a very serious Federal Crime and has some serious consequences.
Under the U.S. Code, a Postal Service officer or employee who “unlawfully secretes, destroys, detains, delays, or opens any letter, postal card, package, bag, or mail entrusted to him or which shall come into his possession, and which was intended to be conveyed by mail, or carried or delivered by any carrier or other employee of the Postal Service” is subject to a criminal penalty of up to five years in prison, a fine, or both.
Thank you.
Now we'll see if reality matches the statute. To make any inroads against vote fraud, people who do this will need to be tried, convicted and imprisoned.