JSFiddle - React, Tailwind, and code Playground
HTML
<a class="mailto">abc</a>
JavaScript
var agencyemail = '[email protected]';
$('a.mailto').prop('href','mailto:' + agencyemail);
<a class="mailto">abc</a>
var agencyemail = '[email protected]';
$('a.mailto').prop('href','mailto:' + agencyemail);