How to disable email field in OptinMonster

Short answer: You can’t do that in an official way.

Luckly, there are the tip:

Go to Advanced Setting => Custom JavaScript, paste this code:

<script>
    document.getElementById('pelican-field-email').value = '[email protected]';
</script>

And in Custom CSS, paste this code:

html div#om-{{id}} #{{ns}}-field-email{
    display: none !important;
}

Done