Reply-To is ignored when both emails are in the same domain

Problem/Motivation

When the from email and the reply-to email belong to the same domain, the "Use Reply-To header" setting is ignored.

For example, we have a site that has hundreds of webforms, each one sends emails from a different user, all of them use the generic address "webmaster@example.com" which authenticates in an email server.
When "john.doe@example.com" configures his webform, the emails are sent from "john.doe@example.com" and not from "webmaster@example.com" as expected when enabling the "Use Reply-To header" setting.
As we use an authenticated email server, these emails are rejected.

The part that produces this behavior is in webform.submissions.inc:

    if (webform_variable_get('webform_email_replyto') &&
        empty($email['headers']['Reply-To']) &&
        ($default_from_name = webform_variable_get('webform_default_from_name')) &&
        ($default_from_address = webform_variable_get('webform_default_from_address')) &&
        ($default_from_parts = explode('@', $default_from_address)) &&
        count($default_from_parts) == 2 &&
        $default_from_parts[1] &&
        stripos($email['from'], '@' . $default_from_parts[1]) === FALSE) {

Specifically, stripos($email['from'], '@' . $default_from_parts[1]) === FALSE will filter out any email addresses that share the same domain. I think if you don't use an authenticated Email server, you will never notice this.

Proposed resolution

Change the condition to only check exact email.