Wordpress - "Reply-to Address" Email

If and when you are using wp_mail(), then you can just set Reply-To for the $headers parameter. Exemplary usage below:

$to          = "abc@def.gh";
$subject     = "Using Reply-To with wp_mail";
$message     = "This is an example for using Reply-To with wp_mail.";
$headers[]   = 'Reply-To: Name Name <ijk@lmn.op>';
$attachments = array();
wp_mail( $to, $subject, $message, $headers, $attachments ); 

There is a hook wp_mail hook too, which you could use to change the parameters.