What Makes a Mailer ‘Letterbox Friendly’? And Why It Matters

If you’re sending products through the post, you’ve likely heard the term “letterbox-friendly”. But what does it actually mean - and why should you care? At Parcelsend UK, we help businesses find the right packaging for every product. And when it comes to lightweight, non-fragile goods, letterbox-friendly packaging can be a game-changer for cost, convenience, and customer satisfaction.

Let’s break down what qualifies as a letterbox-friendly mailer, why it matters for your business, and how to choose the right option.

What Does “Letterbox-Friendly” Actually Mean?

A mailer is considered letterbox-friendly when it meets the standard UK letterbox dimensions - meaning it can be posted through the door without requiring the recipient to be home or answer the door.

Royal Mail Letterbox Size Reference:

• Max thickness: 25mm.
• Max length: 353mm.
• Max width: 250mm.
• Weight limit: Up to 750g.

Any packaging within these dimensions qualifies as a Royal Mail Large Letter, which also makes it more affordable to send compared to small parcels.

Benefits of Using Letterbox-Friendly Mailers

Fewer Missed Deliveries

No one likes to find a “Sorry We Missed You” card on the mat. Letterbox-friendly packaging means your product gets delivered - whether the customer is home or not.

Cheaper Postage

Large Letters cost significantly less than Small Parcels when sending via Royal Mail. This helps keep your fulfilment costs down, especially at volume. And if you use a franking machine, these postage savings are even larger.

Happier Customers

Convenient delivery = better experience. It’s particularly useful for subscriptions, greeting cards, cosmetics, and smaller e-commerce items.

Eco & Space Efficient

Smaller packaging means less material, less waste, and lower emissions during delivery - all positives for environmentally conscious brands.

Best Packaging Types for Letterbox-Friendly Delivery

Large Letter Boxes

Rigid, slim cardboard boxes designed specifically to meet Royal Mail's Large Letter size guidelines. These are ideal for small electronics, subscription products, printed goods, or grouped orders that need more structure than a bag or envelope can offer. View our range of Large Letter boxes here.

Padded Envelopes

Perfect for protecting delicate or lightweight items such as tech accessories, jewellery, and small beauty products. These are available in a variety of colours and a range of different sizes which fall into the Royal Mail Large Letter category. View our range of padded envelopes here.

Board-Backed or Cardboard Envelopes

For flat products like books, prints, or documents. Keeps them rigid and crease-free while staying under the 25mm height. These are available in a range of different sizes which fall into the Royal Mail Large Letter category. View our range of cardboard envelopes here.

Paper Mailing Bags

Eco-friendly and ideal for clothing, accessories, or stationery. Flexible enough to hold soft items and remain slim. These are available in a range of different sizes which fall into the Royal Mail Large Letter category. View our range of paper mailing bags here.

Tips for Making Sure Your Mailer Stays Letterbox-Friendly

• Check the thickness after packing - don't go over 25mm.
• Use lightweight void fill if needed, like tissue or shredded paper.
• Consider flat-packing or rolling soft items like t-shirts.
• Always test your mailers with your products before bulk-buying.

Final Thoughts

Letterbox-friendly packaging isn’t just about meeting a size guideline - it’s about providing a better customer experience while saving your business money on delivery and returns.

At Parcelsend UK, we stock a wide range of letterbox-friendly options to suit different product types, materials, and brand values - from eco mailers to protective envelopes and beyond. View our range of Royal Mail Large Letter here. You can also view our range of packaging supplies here.