Tamper-Evident Postal Packaging Our M3 cardboard envelope mailer is one of the largest sizes in the Lil "M-Spec" range that still fits Royal Mail's large letter tariff, purpose built for A4 documents, magazines, and larger paperbacks that need more protection than a poly mailer but don't need a full box. Made from strong corrugated kraft cardboard, the M3 offers box form rigidity in a slim, letterbox friendly format. Pre folded flaps and ghost creases mean fast, consistent packing every time, and the peel and seal tear strip closure means you can seal orders without tape. Designed to accommodate Royal Mail's large letter tariff flat packed (249 x 352mm), extremely close to the tariff's maximum allowed dimensions, or the small parcel tariff when expanded (268 x 179 x 70mm), helping you keep postage costs down whichever way you pack it. (See our guide to large letter tariff savings for the full postage breakdown.) Our peel and seal closure uses a high tack adhesive that bonds permanently on contact, unlike lower security seals that can be carefully peeled back and reapplied without obvious signs of tampering. Once sealed, our mailers are tamper evident: any attempt to open the parcel in transit leaves a clear, visible mark, giving your customers confidence that what arrives is exactly what was sent. Ideal for: A4 documents, magazines, larger paperbacks, brochures, and other larger flat or lightly bulky items. Lil Packaging is Europe's largest independent producer of ecommerce postal packaging. See more of our M-Range Cardboard Mailers. Product Specification: Size: 249 x 352mm (flat pack) / 268 x 179 x 70mm (expanded) Material: Corrugated kraft cardboard Closure: Peel & seal, tamper evident Postal fit: Royal Mail Large Letter (flat, maximiser size) / Small Parcel (expanded) Certifications: FSC®, Plastic Free, Zero Carbon Why choose the M3: 100% recyclable, FSC® certified, plastic free Zero Carbon manufacturing (UK made) Peel and seal closure, no tape needed Reinforced corners reduce in transit damage
