Sends a confirmation request email when a change of user email address is attempted.

function send_confirmation_on_profile_email() {
	global $errors;

	$current_user = wp_get_current_user();
	if ( ! is_object( $errors ) ) {
		$errors = new WP_Error();
	}

	if ( $current_user->ID != $_POST['user_id'] ) {
		return false;
	}

	if ( $current_user->user_email != $_POST['email'] ) {
		if ( ! is_email( $_POST['email'] ) ) {
			$errors->add(
				'user_email',
				__( 'Error: The email address is not correct.' ),
				array(
					'form-field' => 'email',
				)
			);

			return;
		}

		if ( email_exists( $_POST['email'] ) ) {
			$errors->add(
				'user_email',
				__( 'Error: The email address is already used.' ),
				array(
					'form-field' => 'email',
				)
			);
			delete_user_meta( $current_user->ID, '_new_email' );

			return;
		}

		$hash           = md5( $_POST['email'] . time() . wp_rand() );
		$new_user_email = array(
			'hash'     => $hash,
			'newemail' => $_POST['email'],
		);
		update_user_meta( $current_user->ID, '_new_email', $new_user_email );

		$sitename = wp_specialchars_decode( get_option( 'blogname' ), ENT_QUOTES );

		/* translators: Do not translate USERNAME, ADMIN_URL, EMAIL, SITENAME, SITEURL: those are placeholders. */
		$email_text = __(
			'Howdy ###USERNAME###,

You recently requested to have the email address on your account changed.

If this is correct, please click on the following link to change it:
###ADMIN_URL###

You can safely ignore and delete this email if you do not want to
take this action.

This email has been sent to ###EMAIL###

Regards,
All at ###SITENAME###
###SITEURL###'
		);

		/**
		 * Filters the text of the email sent when a change of user email address is attempted.
		 *
		 * The following strings have a special meaning and will get replaced dynamically:
		 * - ###USERNAME###  The current user's username.
		 * - ###ADMIN_URL### The link to click on to confirm the email change.
		 * - ###EMAIL###     The new email.
		 * - ###SITENAME###  The name of the site.
		 * - ###SITEURL###   The URL to the site.
		 *
		 * @since MU (3.0.0)
		 * @since 4.9.0 This filter is no longer Multisite specific.
		 *
		 * @param string $email_text     Text in the email.
		 * @param array  $new_user_email {
		 *     Data relating to the new user email address.
		 *
		 *     @type string $hash     The secure hash used in the confirmation link URL.
		 *     @type string $newemail The proposed new email address.
		 * }
		 */
		$content = apply_filters( 'new_user_email_content', $email_text, $new_user_email );

		$content = str_replace( '###USERNAME###', $current_user->user_login, $content );
		$content = str_replace( '###ADMIN_URL###', esc_url( admin_url( 'profile.php?newuseremail=' . $hash ) ), $content );
		$content = str_replace( '###EMAIL###', $_POST['email'], $content );
		$content = str_replace( '###SITENAME###', $sitename, $content );
		$content = str_replace( '###SITEURL###', home_url(), $content );

		/* translators: New email address notification email subject. %s: Site title. */
		wp_mail( $_POST['email'], sprintf( __( '[%s] Email Change Request' ), $sitename ), $content );

		$_POST['email'] = $current_user->user_email;
	}
}