My company and one of our business partners were both using hosted Exchange with a particular vendor. The business partner moved to a different hosted Exchange vendor a couple weeks ago; my company is still with the original vendor. Since the move, the business partner doesn't receive email from my company. We don't get delivery failures but the emails just never show up in their inboxes (or spam or junk). The business partner receives email successfully from all other domains. The MX records were updated properly as far as I can tell. The two vendors are pointing fingers at each other. Any advice?