Passster: Send e-mail one day before password expires.

functions.php

<?php

add_action( 'passster_compare_expiration_date', function( $password, $difference, $password_list_id ) {
	if ( $difference == 1 ) {
		// prepare and send the e-mail.
		$to      = '[email protected]';
		$subject = 'Password ' . $password . 'was used';
		$headers = array( 'Content-Type: text/html; charset=UTF-8' );
		$body    = 'Password ' . $password . ' form passwords list ' . $password_list_id . ' will expire tomorrow';

		// Now we can send the e-mail.
		wp_mail( $to, $subject, $body, $headers );
	}
}, 3, 10 );