ICTS are doing some work on the Exchange email server this evening.
Here is their communication on this:

“Between 7.00pm and 9.00pm tonight (20th October 2014) there will be brief periods of email outage or slow performance of the Exchange email servers whilst a critical security patch is applied for the SSL3 vulnerability.

If any issues occur after the patching is completed, please restart the mail client e.g. Outlook. If issues continue after the mail client is restarted, please contact the ICT Service Desk.”