At this time, Microsoft is experiencing email sending failures from accounts that have been flagged for the suspecting sending of spam, or possibly fell victim to a phishing attempt.
Microsoft is aware of the problem and is currently working on a resolution. Users experiencing this issue will receive this message when an email fails to send:
"Your message couldn't be delivered because you weren't recognized as a valid sender. The most common reason for this is that your email address is suspected of sending spam and it's no longer allowed to send messages outside of your organization. Contact your email admin for assistance."
If you are have received an email like this, contact the Help Desk and we can assist in unlocking your account. If you have questions, please contact the Help Desk at (937) 775-4827.