Mailto Attachment Parameter: Support Matrix
How do modern web browsers, webmail services, and desktop email clients handle parameters like ?attachment=? Here is the detailed technical breakdown.
Client Capability Matrix
| Email Client | Support Status | Technical Explanation |
|---|---|---|
| Gmail (Web App) | ❌ Unsupported | Web applications are strictly sandboxed. Gmail web cannot gain access to your local filesystem to grab files. |
| Outlook.com (Web App) | ❌ Unsupported | The web interface ignores any attachment queries for security and compatibility across different browsers. |
| Outlook (Desktop App) | ⚠️ Proprietary / Legacy | Older local desktop installations in legacy internal configurations historically supported private flags, but modern setups ignore it entirely. |
| Apple Mail (Mac & iOS) | ❌ Unsupported | Ignores unrecognized parameters. Using web-triggered attachment queries is not a reliable standard web solution. |
| Mozilla Thunderbird | ❌ Unsupported | Does not parse custom attachment properties. This parameter is not a reliable standard web solution. |
Why Parameter Mapping Fails
Unlike variables like subject or body which only carry URL-encoded text payload, an attachment requires a reference to a binary object. Even if a link could successfully pass a file path (e.g., ?attachment=C:/docs/invoice.pdf), web browsers have no mechanism or permission to upload or attach that file on behalf of the user.
If you need a reliable method to send files through web forms or links, you must utilize alternative methods.
Recommended Workaround
Upload the file to cloud storage (Google Drive, Dropbox) and insert the link inside the body parameter.