Bad value “mailto:X” for attribute “href” on element “a”: Illegal character after “ilto:”. “<” is not allowed.

The mailto: link in this href contains a < character, which is not allowed in a URL. It usually appears when an email is pasted in Name <address> form, or when two addresses are joined without a proper separator.

A mailto: URL holds one or more bare email addresses after the colon, nothing else. Angle brackets, spaces, and the Display Name <address> notation used by email clients are not valid URL characters, so the validator rejects the link at the first illegal character. An encoded space (%20) followed by a second copy of the address, as in this case, is a typical sign that a Name <address> string or a pair of addresses was copied straight into the attribute.

To fix it, keep only the address itself. Drop the display name and the angle brackets, and if the link targets several people, separate the addresses with commas.

Invalid example

<a href="mailto:info@example.com%20<info@example.com">Email us</a>

Valid example

A single recipient needs only the bare address:

<a href="mailto:info@example.com">Email us</a>

For more than one recipient, separate the addresses with commas:

<a href="mailto:info@example.com,research@example.com">Email us</a>

Learn more:

MDN Reference

MDN - The a element

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www.rfc-editor.org

RFC 6068 - The mailto URI scheme

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MDN Reference

MDN - Percent-encoding

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