Wow! Well, you got it working, but God that's ugly.
I'd still be tempted to raise a service request with them.....cos the api doesn't work as specced out in mailinator's requirements....and they need to know that....although i seriously doubt they don't know about it tbh.
Sorry i couldn't straighten it out for you, but at least you've found a workaround,
if this helped answer the post, could you please mark it as 'solved'? Also if you consider whether the title of your post is relevant? Perhaps if the post is solved, it might make sense to update the Subject header field of the post to something more descriptive? This will help people when searching for problems. Ta