Dear Customer,
The Exchange Server datacentre will be performing Microsoft Software that require rebooting your server. Individual services should only be unavailable long enough for patch installation and reboot. Incoming messages will be queued until maintenance is completed.
Maintenance Window Start: Wednesday, March 27, 2013 2PM SGT
Maintenance Window End: Wednesday, March 27, 2013 6PM SGT
Expected Downtime: 15 Minutes
Regards
Microsoft Exchange Cloud Team