There is no problem really with using the method == post trigger, it just means that if I had my own page on my site and set the action of the form to this page on your site and set the method to post I will trigger the server behavior. There is no check to confirm that the user on the page initiated the post.
If you are getting a proper result and feel ok with using just the check for post then that should be fine. The reason I suggested this additional condition was to check to see if the register button was pressed. It should post an element with the name of the submit button and it should be set to whatever you specify as the value for the submit button. Are you testing this with Internet Explorer? If so it could account for the message not getting sent with the updated code. There is a problem when submitting forms via images sometimes in IE and the name of the element will not be passed as part of the post.
If you are experiencing this issue the way to resolve it and use the check for Register posting is to add a new hidden form element to your form and give it the same name as the button and set it's value like this:
<input type="hidden" name="Register" id="Register" value="1"/>
If you have trouble using this additional check for register posting then it might be best for you to just check for post.