We perform maintenance on the mail service systems to provide optimal performance and security. Maintenance sometimes causes downtime, but usually does not.
If we expect a maintenance event to cause downtime we will use reasonable efforts to post notice of the maintenance in advance. For example, if we have to remove a system element to perform maintenance, we will transfer the system to a redundant element to minimize downtime, but there will be some downtime while the system transfers to the redundant element.
If maintenance is urgently needed, we may not be able to give much, or any, advance notice; for example, we may need to install critical security updates or replace failed system components.