Family Law Questions? Ask a Family Lawyer Online.
What kind of mail is it?
Does it specially state to be opened by the addressee only?
Thank you for the clarification.
Yes, It is illegal to open another person's mail. It is actually a federal offense because the mail is sent through the United States Postal Service.
You should start by filing a complaint with the United States Postal Service:
Thanks for the ACCEPT.
I have additional link for you:
All the best,