About This HTML Issue
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:
-
Check the email address for typos. Remove any accidental spaces in the local part (before
@) or the domain part (after@). -
Percent-encode spaces in query parameters. If you’re using
subject,body, orccparameters in themailto:URI, replace spaces with%20. - 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:
<a href="mailto:user@example com">Send Email</a>Valid — corrected email address
Remove the space to form a valid email address:
<a href="mailto:user@example.com">Send Email</a>Invalid — space in the local part
<a href="mailto:john doe@example.com">Send Email</a>Valid — space removed from local part
<a href="mailto:johndoe@example.com">Send Email</a>Invalid — unencoded spaces in subject parameter
<a href="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:
<a href="mailto:info@example.com?subject=Hello%20World">Email Us</a>Valid — full mailto with multiple parameters
<a href="mailto:support@example.com?subject=Bug%20Report&body=Please%20describe%20the%20issue.">
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