For trivial protection against dumb email address crawlers, write <a href=mailto:me(at)example(dot)org>me(at)example(dot)org</a> and include this JS at the bottom of the page.

mailto-es6.js

// jshint esversion: 6, maxlen: 80, strict: global

'use strict';

// In mailto: links, replace '(at)' with '@' and '(dot)' with '.'
{
    const at = /\(at\)/gi;
    const dot = /\(dot\)/gi;
    const links = document.querySelectorAll('a[href^="mailto:"]');

    for (let link of links) {
        link.href = link.href.replace(at, '@').replace(dot, '.');
        link.innerHTML = link.innerHTML.replace(at, '@').replace(dot, '.');
    }
}

mailto.js

// jshint maxlen: 80, strict: global

'use strict';

// In mailto: links, replace '(at)' with '@' and '(dot)' with '.'
(function (d) {
    var at = /\(at\)/gi;
    var dot = /\(dot\)/gi;
    var link;
    var links = d.querySelectorAll('a[href^="mailto:"]');
    var i;
    var max;

    for (i = 0, max = links.length; i < max; i++) {
        link = links[i];
        link.href = link.href.replace(at, '@').replace(dot, '.');
        link.innerHTML = link.innerHTML.replace(at, '@').replace(dot, '.');
    }
})(document);

mailto.min.js

(function(a){var c=/\(at\)/gi,d=/\(dot\)/gi,e=a.querySelectorAll('a[href^="mailto:"]'),f;var b=0;for(f=e.length;b<f;b++)a=e[b],a.href=a.href.replace(c,"@").replace(d,"."),a.innerHTML=a.innerHTML.replace(c,"@").replace(d,".")})(document);