About This HTML Issue
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
<a href="mailto:<user@example.com>">Email us</a>
Correct
<a href="mailto:user@example.com">Email us</a>
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