Delivered to your home I assume? Are you sure that's legal? .
It most definitely is not legal. Go to any site that sells on line; if they do not specifically list Maryland as a place they won't ship mags over 20rd (most list the states) then they will have this general disclaimer instead:
We only ship to states that it is legal to have 30rd magazines.
That said, I'm aware of occasions where mags over 20 rds were shipped through the mail to MD addresses, even though the seller had stated prior that the mags could not be shipped to MD and would have to be removed from the order.
It's crazy out there.