trim any spaces at the start of the text box and trim any spaces at the end of the textbox.

trim_input_onchange.html

<script>

function trim(el){
    el.value = el.value.
       replace (/(^\s*)|(\s*$)/gi, ""). // removes leading and trailing spaces
       replace (/[ ]{2,}/gi," ").       // replaces multiple spaces with one space
       replace (/\n +/,"\n");           // Removes spaces after newlines
    return true;
}
</script>

<input type="text" name="email" id="_email" pattern=".{3,}@.{3,}\..{2,5}" onchange="return trim(this)" required="required"  class="input input_email" placeholder="Email Address *">