What the code contains
A mailto: link, which is the same thing behind every email link on the web:
mailto:hello@example.com?subject=Enquiry&body=Hi%2CThree parts: the address, an optional subject, an optional body. The phone recognises themailto: prefix and hands it to the default mail app, which opens a composer with everything already in place.
It composes, it never sends. The person still has to press send, and can edit anything you pre-filled before they do. That is worth knowing if you were planning to put something in the body you would not want changed.
The subject line is the whole trick
A bare address in a code is barely better than a bare address in print. The subject is what makes it useful, because it arrives in your inbox already sorted:
- "Enquiry — trade fair stand" on the stand banner.
- "Quote request — kitchen" on the showroom card.
- "Fault report — machine 14" on the machine itself.
- "Application — warehouse role" on the recruitment poster.
Print a different code per location and every message tells you which one earned it. That is campaign attribution with no tracking service, no redirect and no analytics — the sender is telling you directly, and they never had to be tracked to do it.
Keep the body short, or empty
Everything you pre-fill lives inside the pattern. A subject costs you a handful of characters. A paragraph of body text can push a comfortable version 4 code up past version 10, which needs roughly three times the print area to stay readable.
If you want to prompt the sender, one line does it — "Please include your postcode" — and it survives at a printable size. If you find yourself writing a form, you want a form, and aGoogle Form code is the better tool.
Where it beats a phone number
Email suits the enquiries that are not urgent and that benefit from a written record: quotes, specifications, applications, complaints, anything with an attachment. It is also the polite option for a stranger — writing costs them nothing socially, where a phone call costs quite a lot.
The reverse is also true. If the next step is a five-minute conversation, aphone code or aWhatsApp code gets there faster.
About spam
The common worry is that a code exposes your address to harvesters. On print it does not, in any practical sense — address harvesters crawl web pages, and nobody is running a scraper that photographs posters.
On a web page it is a different question, but not because of the code: if the code is on your site, the address is in your page source too, and that is what gets read. A code changes nothing either way there.
Print the address as well
Always. Some people will not scan an unfamiliar code, some cameras will not parsemailto:, and some phones have no mail app configured at all — in which case the scan does nothing and the person has no idea why. The written address costs you one line and removes the whole failure class.