Large Family celebration mailbox covers from Flagsrus for all occasions. Weddings, Anniversaries, Graduation, Births, Birthdays and more. Flagsrus offers high quality, large magnetic mailbox covers from Magnet Works (Studio M). Add a splash of color with a vinyl weather resistant mailbox cover! All covers feature a slot for the postal carrier alert flag. These covers attach to the mailbox with magnets. The large size fits 8" x 21" mailboxes. No worry if you have a plastic or aluminium box, see the Adapter Kit.