I am Matt Bushnell and will try to assist you. It is my understanding that within Office 365 and when hosted by them, that there is a SPAM email protection in place that would stop spamming applications from being able to send bulk email. If you would like I can try to research this and see if there is anything that can be done. It will be sometime tomorrow by mid afternoon if that is okay. If not let me know and I will opt out and allow another expert to assist. Just let me know.
Thank you and I will be in touch by tomorrow afternoon.