HTML Guides for mailto

A mailto: link must not contain spaces between the colon and the email address.

The href attribute on an <a> element accepts mailto: URLs as defined in RFC 6068. The email address must immediately follow the colon with no whitespace. Browsers may still attempt to open the mail client, but the space makes the URL technically invalid and triggers a W3C validation error.

This applies to all parts of the mailto: URL. Spaces before the address, between multiple addresses, or before query parameters like ?subject= are all invalid. If you need to include a space in a subject or body parameter, encode it as %20.

HTML examples

Invalid

<ahref="mailto: user@example.com">Email us</a>

Valid

<ahref="mailto:user@example.com">Email us</a>

A < character inside an href attribute is not valid in a URL and must be removed or percent-encoded.

The mailto: URL scheme expects a well formed email address directly after the colon, such as mailto:user@example.com. The angle brackets (< and >) sometimes seen around email addresses in mail headers or plain text are not part of the URL syntax. Including them in the href value produces an illegal character error because < and > are not permitted in URIs without percent-encoding.

If angle brackets appear in your markup, they likely got there by copying an address from an email header like From: User <user@example.com> and pasting the whole thing into the link. Strip the brackets so only the bare address remains.

HTML examples

Incorrect

<ahref="mailto:<user@example.com>">Email us</a>

Correct

<ahref="mailto:user@example.com">Email us</a>

A mailto: link follows URI syntax as defined by RFC 3986, which does not permit raw space characters anywhere in the URI. When the W3C validator encounters a space inside the href value of a mailto: link, it reports it as an illegal character in the scheme data. This most commonly happens due to a typo in the email address itself — for example, accidentally inserting a space in the domain name (example .com) or the local part (user name@example.com). It can also occur when query parameters like subject or body contain unencoded spaces.

This matters for several reasons. First, browsers may truncate or misinterpret the href at the space boundary, meaning the mail client may open with an incorrect or incomplete email address. Second, assistive technologies rely on well-formed URIs to communicate link destinations to users. A malformed mailto: link can confuse screen readers or prevent users from understanding where the link leads. Third, invalid markup signals poor quality to search engines and automated tools.

To fix this issue:

1. Check the email address for typos. Remove any accidental spaces in the local part (before @) or the domain part (after @).
2. Percent-encode spaces in query parameters. If you're using subject, body, or cc parameters in the mailto: URI, replace spaces with %20.
3. Avoid copying and pasting email addresses from formatted documents, which can introduce non-breaking spaces or other invisible whitespace characters.

Examples

Invalid — space in the email address

A space in the domain name makes the URI invalid:

<ahref="mailto:user@example com">Send Email</a>

Valid — corrected email address

Remove the space to form a valid email address:

<ahref="mailto:user@example.com">Send Email</a>

Invalid — space in the local part

<ahref="mailto:john doe@example.com">Send Email</a>

Valid — space removed from local part

<ahref="mailto:johndoe@example.com">Send Email</a>

Invalid — unencoded spaces in subject parameter

<ahref="mailto:info@example.com?subject=Hello World">Email Us</a>

Valid — percent-encoded spaces in subject parameter

Replace each space with %20 in query parameter values:

<ahref="mailto:info@example.com?subject=Hello%20World">Email Us</a>

Valid — full mailto with multiple parameters

<ahref="mailto:support@example.com?subject=Bug%20Report&body=Please%20describe%20the%20issue.">

Report a Bug

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