CRL No-Draft Mail Slot

Insulated Mail Slot mail slot insulation This premium quality, weather-resistant aluminum Draft Dodger mail slot comes with an insulating rubber seal that blocks drafts and an interior brush mail slot in door INSULATED MAIL SLOT – DELUXE 46100, 46200 # 461001 When the slot is closed, the cylinder becomes a sealed air-chamber providing excellent thermal insulation

mail slot mailbox This right here is the best answer You can also glue some thin insulation to the magnet sheet if it is really bad