What is a mailto: URI?

A mailto: URI, defined in RFC 6068, is a link that opens the user's email client with a new message pre-filled. Putting it in an anchor's href lets a click compose an email to a chosen address with an optional subject and body.

How are spaces and line breaks handled?

All header values are percent-encoded. Spaces become %20 and a line break becomes %0D%0A (a carriage return plus line feed), which is the correct sequence for the body of a mailto link so paragraphs render properly.

Can I add Cc and Bcc?

Yes. Cc and Bcc are added as query parameters after the subject and body, each holding one or more comma-separated addresses. Bcc recipients are not shown to other recipients when the message is sent.

Why is the subject encoded but the email address mostly not?

The address sits in the URI path and only its reserved characters are escaped, while the subject and body are query values where spaces, ampersands and other characters must be percent-encoded so the link parses correctly.

No. The mailto link is assembled entirely in your browser, so nothing you type is sent to a server.

What is the Mailto URI Encoder?

Free mailto: URI builder — generate a valid RFC 6068 mailto link with cc, bcc, subject and body, all properly percent-encoded, instantly in your browser. It runs free in your browser on Gera Tools, with nothing uploaded.

Mailto URI Encoder — Gera Tools

Name: Mailto URI Encoder
Creator: Gera Tools
License: https://creativecommons.org/licenses/by/4.0/

The mailto: URI encoder builds a valid RFC 6068 mailto: link from a recipient list plus optional Cc, Bcc, subject and body. Each field is percent-encoded correctly so the link survives in HTML, QR codes and chat messages, and opens the user’s mail client with everything pre-filled.

How it works

A mailto link has the form mailto:address?key=value&key=value. The To addresses sit before the ?; additional recipients and the message use query parameters cc, bcc, subject and body. RFC 6068 requires that values be percent-encoded: every byte that is not an unreserved character is replaced with % plus its two-digit hex code.

The encoder uses encodeURIComponent for each value, then fixes the special cases the standard calls out — line breaks in the body must be %0D%0A, and a few characters are left readable. Parameters are joined with &. Empty fields are omitted, so a To-only link is simply mailto:[email protected].

What each field does

To — the primary recipient address(es). Multiple addresses are comma-separated in the URI. Most mail clients accept Name <email> syntax if URL-encoded properly, but plain addresses are the most compatible.

Cc — carbon copy. Recipients in Cc see each other’s addresses and receive the same message. Encoded as the cc query parameter.

Bcc — blind carbon copy. Bcc recipients receive the message but are not visible to To or Cc recipients. Browser mailto support for Bcc varies significantly — some clients honour it, others ignore the field entirely. Test with your target client.

Subject — pre-fills the subject line. Spaces encode as %20; special characters like &, =, and # are percent-encoded.

Body — pre-fills the message body. Line breaks must be %0D%0A (CRLF) per the RFC, not just %0A. This tool handles that encoding automatically.

Worked example

To:      [email protected]
Cc:      [email protected]
Subject: Hello there
Body:    Line one
         Line two

Output:
mailto:[email protected]?cc=team%40example.com&subject=Hello%20there&body=Line%20one%0D%0ALine%20two

The @ in the Cc address is encoded as %40 because it sits inside a query parameter value. In the To position (before the ?) it can appear unencoded.

Where to use mailto links

Website contact buttons: <a href="mailto:[email protected]?subject=Help">Email us</a> opens a pre-addressed compose window.
HTML email signatures: embed a pre-filled feedback or reply link.
QR codes: a mailto URI in a QR code opens the compose window on mobile. Shorter bodies work better here since QR data density limits apply.
React and front-end apps: window.location.href = 'mailto:...' triggers the mail client. Some browsers block this for non-user-initiated events.
Markdown documentation: [Open issue](mailto:[email protected]?subject=Bug%20report) works in most Markdown renderers.

Limitations to be aware of

URL length: browsers cap URL length (commonly 2048–8192 characters). Long pre-filled bodies may be silently truncated. Keep bodies under roughly 1,500 characters for broadest compatibility.
Bcc: not universally respected by all email clients. Outlook, Apple Mail, and Thunderbird handle it differently. If Bcc is critical, test before relying on it.
HTML vs. plain text: mailto links produce plain-text compose windows. If you need to pre-fill HTML formatted email, mailto is not the right tool.
Webmail clients: Gmail, Outlook.com, and other web-based clients typically intercept mailto links only if the user has set them as the default handler in their browser.

Notes

Everything runs locally; nothing you type is uploaded. The output drops straight into <a href="mailto:..."> or any other context that accepts a URI.