a very simple and effectively way to hide email from spam bots

encode-decode-email.php

<?php
$email = '[email protected]'; // when email-domain-part contains umlauts, use the idn format: idn_to_ascii('your-email@example-äöü.com');
$emailLength = mb_strlen($email);
$randomFactor = '';
$encodedMail = '';

for ($ix = 0; $ix < $emailLength; $ix++) {
    $randomFactor .= rand(1, 9);
}

foreach (str_split($email) as $currentIndex => $c) {
    if ($c !== '@') {
        bendIntoShapeCurrentCharacter($randomFactor, $c, $currentIndex);
        $encodedMail .= encodeCharacter($c, str_split($randomFactor)[$currentIndex]);
    } else {
        $encodedMail .= '@';
    }
}

function encodeCharacter($character, $factor) {
    $charCode = mb_ord($character);
    $charEncoded = $charCode + $factor;
    return mb_chr($charEncoded);
}

function bendIntoShapeCurrentCharacter(&$randomFactor, $c, $currentIndex) {
    if (preg_match('/[^\w\.]+/i', encodeCharacter($c, str_split($randomFactor)[$currentIndex]))) {
        $randomFactor[$currentIndex] =  rand(1, 9);
        bendIntoShapeCurrentCharacter($randomFactor, $c, $currentIndex);
    }
}
?>

<a id="email" href="mailto:<?= $encodedMail; ?>">encodeded E-Mail</a>
<script src="https://ajax.googleapis.com/ajax/libs/jquery/3.4.1/jquery.min.js"></script>
<script>
    (function($) {
        'use strict';
        let factor = "<?= $randomFactor; ?>";

        function decodeCharacter(character, factor) {
            return String.fromCharCode(character.charCodeAt(0) - factor);
        };

        // Hide Email Address from Spambots, decode mechanism
        function replaceMailTo() {
            let element = this;
            let tmp = JSON.parse(JSON.stringify(element));
            let currentMail = $(element).attr('href').split(':')[1];

            let decodedMail = '';
            let index = 0;
            currentMail.split('').forEach(function(c) {
                if (c !== '@') {
                    decodedMail += decodeCharacter(c, factor.split('')[index]);
                } else {
                    decodedMail += '@';
                }

                index++;
            });
            
            // optional subject
            decodedMail += '?subject=your-subject...';
            element.setAttribute("href", 'mailto:' + decodedMail);
            $(element).removeAttr("id");
        };

        $(document).on('click', '#email', replaceMailTo);
    })(jQuery);
</script>