邮件QR Code：扫描时预填充消息
Creating mailto: QR codes with pre-filled recipient, subject, and body. URL encoding, length limits, and client compatibility.
Email QR Codes: Pre-filled Messages on Scan
Email QR codes encode a mailto: URI that opens the user's email client with pre-filled recipient, subject, and body text. They bridge the gap between physical media and digital communication.
The mailto: URI Format
mailto:[email protected]?subject=Hello&body=I%20have%20a%20question
| Parameter | Description | URL Encoding |
|---|---|---|
| Recipient | Email address (before ?) |
Standard |
subject |
Pre-filled subject line | Percent-encoded |
body |
Pre-filled message body | Percent-encoded |
cc |
Carbon copy recipients | Comma-separated |
bcc |
Blind carbon copy | Comma-separated |
URL Encoding Requirements
Spaces, line breaks, and special characters must be percent-encoded:
- Space →
%20 - Line break →
%0A - Ampersand →
%26
This encoding increases the data length, so keep subjects and body text concise to avoid large QR codes.
Length Considerations
The mailto: URI has practical length limits. Most email clients handle up to about 2,000 characters, but the QR code itself must encode this entire string. A mailto: link with a 500-character body at EC Level M requires Version 14 — a large, dense code.
Recommendation: Keep the body under 100 characters and use the subject line to provide context. If more content is needed, link to a web form instead using a URL QR code.
Email Client Compatibility
| Platform | Default Client | Support |
|---|---|---|
| iOS | Mail app | Full mailto: support |
| Android | Gmail or default | Full support |
| macOS | Mail or default | Full support |
| Windows | Outlook or default | Full support |
Users with multiple email accounts may need to select which account sends the message.
Use Cases
- Customer support: Pre-filled subject with product name or order number
- Event RSVP: One-scan response with pre-filled details
- Feedback forms: Subject pre-set to "Feedback" with location identifier
- Business cards: Alternative to phone — "Scan to email me"
Best Practices
- Always include a
subjectto provide context for the recipient - Keep the
bodyshort — use it for a template, not a full message - Test across iOS and Android email clients
- Consider a URL QR code linking to a web form for longer interactions
- Validate the email address before generating the QR code
Key Takeaways
- Email QR codes use the
mailto:URI with optional subject and body - Special characters require percent-encoding, which increases QR code size
- Keep content concise — long body text creates large, hard-to-scan codes
- All major platforms support mailto: URIs natively
- For complex forms, prefer a URL QR code linking to a web-based form