Delivery of Inbound Emails During Planned and Unplanned Salesforce Downtime
Salesforce occasionally has planned (maintenance announced on trust.salesforce.com) and unplanned downtime. Email to Case Premium leverages Apex Email Services, a Force.com platform feature, and has no control over the delivery of email during downtime. Salesforce has made some provisions to ensure email is delivered during downtime.
During planned downtime, Salesforce queues inbound emails destined for Email to Apex routing addresses and the email is delivered when the maintenance is complete.
During unplanned downtime, inbound emails can be handled 1 of 3 ways depending on the nature of the Salesforce outage and how your Apex Email Service is configured. Unfortunately, Salesforce doesn't provide any official documentation on this and it is largely based on our experience during past events. Because inbound emails don't reach Email to Case Premium during Salesforce downtime, planned, or unplanned, we have no control over what happens to emails during this time.