When to use it
Feedback requests on packaging, “report a fault” labels on equipment, a support address on a manual, competition entries. A pre-filled subject line means the reply lands in the right inbox and you can sort messages by which code was scanned.
How it behaves on phones
iPhone: the Camera app shows a banner naming the address. Tapping it opens the default mail app, which is Mail unless the person has changed it to Gmail or Outlook, with a draft ready to edit.
Android: most Android scanners open a chooser if more than one mail app is installed, then the draft. Google Lens shows the address first and offers “Send email”.
If the phone has no mail account set up, nothing useful happens. That is more common than it sounds on work phones and children’s devices.
Common mistake
Writing mailto:hello@example.com?subject=Please send me the brochure. The spaces break the link on some phones so the subject stops at “Please”. Encode it as subject=Please%20send%20me%20the%20brochure.
Gotchas
Encoding. Everything after the question mark must be URL encoded. Space becomes %20, line break %0A, ampersand %26, question mark %3F. Get one wrong and the mail app either truncates the field or shows the raw code.
Length. A long pre-filled body makes a dense code. mailto: plus an address and a short subject is about 50 characters and fits version 3, 29 modules wide. A three sentence body can push it past version 8. Keep the body to a prompt such as “Order number:” and let the person type.
Multiple recipients. Separate them with commas after mailto:. Some older scanners only pass the first one on.
MATMSG. You may see MATMSG:TO:...;SUB:...;BODY:...;; in older generators. It comes from the same Japanese feature phone era as MeCard. Android usually reads it; iPhone does not reliably. There is no reason to use it today.
Try it in QR Studio
QR Studio has an Email type with separate fields for address, subject and body. It encodes spaces and line breaks for you and shows the finished mailto string.
Print advice
Level M. Email codes are usually scanned up close from a leaflet, label or manual, so 2 to 3 cm (1.2 in) is plenty. Print the address in plain text beside the code. A surprising number of people would rather type it, and anyone whose phone has no mail app set up can still reach you.
Try it yourself
Type an address, subject and body, and see the encoded mailto string the code will carry.