Sealing a letterbox in Front Door. How?

[TheMrs]

We live in a Flat that has an external door with a letterbox. All mail is delivered to the main entrance where it is sorted into our mailboxes, therefore the only mail posted through our letterbox is junk mail.

We can't alter the external appearance of the door as the building is listed, but I want to seal the letterbox therefore stopping the posting of any mail through it.

I did have an idea that someone might sell an expanding bolt so I simply placed the bolt in the middle tight in behind the flap and then tightened with a spanner expanding the bolt and thus sealing the letterbox. As far as I know no such bolt is available.

Any ideas on how to achieve my aim?

 

[Burnerman]

Drill a hole through the letterbox flap centre
Insert a bolt slightly longer than the door thickness
Take a strip of metal just longer than the letterbox hole is, and drill a hole in its centre
Pass the bolt through this metal strap, add a nut and tighten up!

Or, gum the thing up with silicone and leave it a while.

Better edit......this would only work with an outward opening flap, of course - for a push in type I'd jam the thing shut with a piece of timber, screwed into the door.

John