Do Franking Machines Need Special Envelopes? 2026 Guide

If you have just started franking your post, one question comes up straight away: do you need special envelopes? The short answer is no. A franking machine prints onto almost any standard envelope, so you are free to use the stationery you already have. That said, a few sensible choices about envelope type, size and weight can protect your postage rates and keep your mailroom running smoothly. This guide explains what works, what to avoid, and when a franking label is the better option.

The short answer: no special envelopes required

A franking machine prints a postal impression, usually in the top right corner of the envelope, in the same way a stamp would sit there. Any clean, flat envelope with enough space in that corner will frank perfectly well. White, manilla, plain and window envelopes all work.

The impression does need a smooth, dry surface to print clearly. Glossy, heavily textured or dark envelopes can cause the ink to smudge or show up faintly, which risks a rejected item. If you post in volume, plain white or manilla envelopes give the most reliable results.

Envelope types that work best

Most businesses choose between gummed and self-seal envelopes. Gummed envelopes need moistening to seal and suit lower volumes or machines with an integrated sealer. Self-seal envelopes close with a peel strip or press flap, which is faster when you are hand-filling a batch.

Window envelopes are also fine to frank. Because the impression prints in the top right and the window usually sits lower left, the two rarely clash. Just check your folded letter shows the address correctly through the window before sealing.

Browse the full range of business envelopes if you want stock that feeds cleanly and franks reliably.

Size and weight decide your postage band

Envelope choice matters most because it affects which Royal Mail format your item falls into, and that sets the price. A Letter must be no larger than 240 x 165 x 5mm and weigh up to 100g. A Large Letter can be up to 353 x 250 x 25mm and up to 750g. Anything bigger or thicker is priced as a parcel.

The gap between the bands is real money. From 7 April 2026, a Mailmark franked Second Class Letter costs 88p, while the same item posted as a Large Letter starts at £1.52. Choosing an envelope that keeps a light document within Letter dimensions, rather than an oversized one, can more than halve the cost. All franked postage prices are exempt from VAT.

When to use a franking label instead

Some items cannot pass through the machine's feed. Thick packets, padded bags and small parcels are too bulky to frank directly, and awkward or uneven envelopes can jam. In those cases you frank onto a self-adhesive label and stick it to the item.

Labels are also useful for busy mailrooms that pre-print postage, and for anything where the surface will not take a clean impression. Keep a supply of franking labels on hand so a bulky item never holds up a post run. Always use labels approved for your machine to stay Mailmark compliant.

Posting after the collection deadline

If you frank mail after your daily Royal Mail collection or posting time, the impression can show the wrong date unless you advance it. To post on the same day after the deadline, many businesses use meter posting envelopes or pouches, which flag the mail for correct handling at the mail centre. It is a small detail that helps avoid items being delayed or returned.

Frequently Asked Questions

Do franking machines need special envelopes?

No. A franking machine prints onto standard business envelopes, including plain, manilla, window and self-seal styles. The only requirement is a clean, flat, light-coloured surface in the top right corner so the postal impression prints clearly. Very glossy, dark or textured envelopes can smudge and are best avoided.

Can you frank window envelopes?

Yes. Window envelopes frank without any problem because the postal impression prints in the top right corner while the address window normally sits in the lower left. Check that your folded letter aligns so the full address is visible through the window before you seal and frank the item.

What is the difference between franking directly and using a franking label?

Franking directly prints the impression straight onto the envelope, which is cheapest and quickest for standard letters. A franking label is a self-adhesive sticker you frank and then apply to items that are too thick or bulky to feed through the machine, such as padded bags and small parcels. Both carry the same valid postage.

Does the envelope size change the postage price?

Yes. Royal Mail prices by format, so a Letter up to 240 x 165 x 5mm is cheaper than a Large Letter up to 353 x 250 x 25mm. Using an envelope that keeps a light document within Letter dimensions can noticeably reduce the cost per item, so match the envelope to the contents.

Franking machines are refreshingly flexible: no special envelopes needed, just clean, flat stationery and the right format for the contents. Get the envelope size right, keep a roll of labels for bulky items, and you will post accurately for less. Explore our envelopes and franking labels to stock up for your next mail run.