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The cutoff is physical: if it is flat, flexible, uniformly thick, and light enough to ride the letter-sorting machines, it can travel as lettermail. Anything lumpy, rigid, or too thick becomes a parcel. Thickness is what catches most people: a padded mailer holding a USB stick or a key is a parcel, not a letter. LetterAgent sells Xpresspost parcel labels, so this guide covers the general question.
Lettermail is built for things that behave like paper: documents, photos, greeting cards, invoices, and anything else that lies flat in a sealed envelope. The item must be rectangular, sealed, flexible enough to bend through sorting machines without damage, and uniform in thickness from edge to edge: no bumps, no clasps, no lumps. A stack of papers in an envelope qualifies. A single sheet with a bulky sticker on it may not. When in doubt, ask yourself whether it would survive being bent slightly by a machine. If the answer is no, it is a parcel.
| Lettermail | Parcel | |
|---|---|---|
| Shape | Flat, rectangular, uniform thickness | Any shape, including boxes and tubes |
| Flexibility | Must bend through letter sorters | Rigid is fine |
| Contents | Paper-like items only | Objects: electronics, keys, coins, pens |
| Tracking | None, unless sent registered | Tracked end to end |
| Typical cost shape | Cheapest option for qualifying items | Higher, but includes tracking and coverage |
Rigidity is the most common tripwire. A USB stick, a coin, a key, or a pen inside a padded mailer turns it into a parcel even though it is small and light: the sorting machines cannot bend around it, and it can jam the equipment. Thickness is the second: beyond the lettermail ceiling, even a stack of pure paper becomes a parcel. Non-rectangular shapes, items tied with string, and envelopes with protruding clasps all fail the machinability test. Counter staff check for exactly these things, and "it fits in an envelope" is not the test: "it survives the sorter" is.
Lettermail has no tracking, and that is not a small detail. If you are selling something, or sending something whose arrival you need to prove, lettermail gives you no evidence it ever arrived. Registered mail adds proof of delivery to a letter-sized item, but for most goods the honest answer is a tracked parcel service. Many sellers learn this the expensive way: they save a few dollars shipping lettermail, the buyer claims it never arrived, and with no scan data there is nothing to argue about. The cheapest shipping option is only cheap if it does the job.
First, see whether the item can be slimmed down. Documents with a rigid insert can often be split: the papers go lettermail, the object goes parcel. Second, flatten: a padded mailer with the air pressed out sometimes fits where a puffy one does not, as long as it stays flexible. Third, be honest about the object: if it contains anything rigid, lumpy, or thick, just buy the parcel label. The surcharge for an item that gets reclassified at the counter (or returned to you) costs more than the parcel rate would have.
Ready to ship it? Get a shipping label with LetterAgent: describe it to your AI assistant, approve the exact quoted price, and get your label.
LetterAgent is a working name. Prices include print, postage, and our service fee. US prices in USD, Canadian prices in CAD (Canadian prices exclude applicable sales tax, added at checkout). Currently in private testing.
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