This raises the question: Is parking in front of someone's mailbox illegal? Tampering with mail delivery is a serious offense, but the legality of parking in front of a mailbox is more complex than it appears. Canva CanvaIs it illegal to park in front of a mailbox in Massachusetts? This can lead to people parking in ways that block mail delivery, making it difficult for mail carriers to access your mailbox. If a car frequently blocks your mailbox and prevents mail delivery, consider contacting the police.