Emails sent to and from your instance are processed by a mail server maintained by ServiceNow. This means that you don't have to manage these servers yourself and worry about connecting them to your ServiceNow database or managing communication between them. Instead, ServiceNow has pre-configured POP3 and SMTP accounts set up to send and receive emails.
These email addresses are formatted like [email protected]. For example, if your instance name (the URL prefix you use to access your ServiceNow instance) is my_company_name, then the email address corresponding to that instance will be [email protected]. Sending an email to this email address will (if inbound email is enabled) result in the existing inbound email actions being evaluated.
You can configure email properties, including turning emails on or off for production or sub-prod instances, by navigating to System Properties | Email Properties.