You can purchase a mailbox kit which has a steel frame and a back plate so it gives you a finished look on the inside. You can try places like this as an example: https://www.mailboxworks.com/ or there is many other sites who carry complete mailbox kits.

Good luck

we have the metal frame on the interior of ours with a flap but its monstrously cold in the winter, so i cover the whole inside part with a square of handsome home dec. fabric, attached at the top and an inch or two down the sides. it provides another later of insulation and doesnt mess with the inside flap. i'm thinking you could do the same for yours, a heavy brocade weight fabric in a color that matches your front entry.

I suggest finding or having made a drawer that would fit snugly and inset to the opening. If you live in a climate that experiences cold or hot temps insulate the drawer. Paint the drawer the same color as the wall and use the knob to hang a wall ornament if you wish.

A little late, but I just found out about this interior grill thing that will solve this problem for us so I thought I'd share. http://store.restoration.com/classic-through-the-wall-mail-slot-inside-grill-65c/dp/117164

Thank you!!

What about an actual frame? Like a vintage gilded/baroque style frame like this? https://www.etsy.com/listing/237497542/mini-frames-ornate-antique-gold-silver

WOW never thought about that. Great Idea. I think I love this. Thank you!

i have the same thing in my home and the original cover is broken.. it is cast iron... i need to find a replacement cover..

I have the same problem!!! I have been looking for a replacement for 2 years!!! Can you shed any light on what you did? I have a 1920s Spanish home and love my inside mailbox drop just hate the opening. I am looking for any kind of grate cover.

Thanks in advance!

I’m looking for the same product. Please update suggestions with new links. The ones from 2016 are no longer available. Please and thank you!

Alisa, you can go on Amazon and look for <mail slot for wall or doors" whichever you need and pick one you like. Some come as a set some you will have to purchase a "mail slot wall sleeve" separately and they're very inexpensive.

I lost my vintage grille and looked high and low for a vintage replacement, and never could find one. Finally, a neighbor who was remodeling their home had one they didn’t need. If you have a vintage home (mine is 1931), I think it honors the home to try to replace that grille with something consistent with the home.