they do have a mail slot draft guard

eBay has this

o you could do something like this pic

Buy another, have a handy man remove the "springs", modify with hinges.

Frankly, the real answer is a box outside the door, unless a no space/safety issue. slots in a door, are best in combination with an AIR LOCK type entry/ door to interior behind the front door: )

oh bummer--too late. YEARS ago my dad removed the mail box from the house, installed a door/opening in the siding near a the garage door--large enough for just about anything..a basket there to catch things and eventually a shelf. Since 99% of the time they come and go through the garage they could just pick up the mail as they came by...no fuss no muss. IDK if those episodes where robbers utilize mail slots to gain access to home are true but this also eliminates any possibility of that.

I guess be happy you get mail deleivery to the door , not where I live . I think the draft guard seems to be not bad. IMO a mailbox outside the door makes sense but is not as secure for sure.