One of our Collab email servers (cecil.collab.uni.edu) has been blocked by Microsoft due to a phished account that was sending out SPAM yesterday evening. Another compromised account was found this afternoon and hopefully dealt with quickly enough to avoid further blacklisting.
ITS has started the process to get us back in Microsoft's good graces, which could take up to 48 hours. Until then, email sent to domains such as live.com, msn.com, and hotmail.com that goes out through cecil will result in failed delivery attempts.