You cannot serve process by mail using a 1st class stamp. You have to use a special class of mail with signature service and return receipt requested, the postal employee does not leave it without an adult who says that they can accept mail for the addressee, signing for it. Also, when you mail it, the process server has to have to physically affix a copy of the suit to the address you are mailing it to, its called nail and mail. Nail it to the door, mail a copy also.
So your anecdote about your neighbors junk mail is irrelevant to this discussion.
thedirt.com got served in error, ignored the papers, and this is what happens when you ignore court papers. This is fixed easily enough by showing up to court now and correcting the error.
The court system works just fine, thedirt.com sitting on their ass and not correcting the error in the beginning is the problem. They would have been able to recover whatever it cost them to respond from the plaintiff that erroneously served them.