wp-includes/ms-deprecated.php:170Deprecated functionality to validate an email address.
$emailstring$check_domainbooloptionaltruestring|falsefunction validate_email( $email, $check_domain = true) { _deprecated_function( __FUNCTION__, '3.0.0', 'is_email()' ); return is_email( $email, $check_domain );}Introduced in MU (3.0.0). Unchanged from 6.7.7 through 7.1.0.
Signature, return type and hooks compared across 5 parsed releases.
src/wp-includes/ms-deprecated.php, and regenerated for each WordPress release so it tracks the code rather than a snapshot of it.