E-mail to hotmail accounts may be rejected until we clear our good name with the service (once again). Yet again, a user has had their account used to send thousands of messages to external entities which has resulted in blacklisting. We will try to clear this up as soon as possible.
In the mean-time, use your UDM account to e-mail other UDM accounts instead of e-mailing to/or from a hotmail account. Sending to accounts within the University domain are gaurenteed delivery.