Firewall rules are often a factor for proper network communication between the MAGE agent and the cloud. A URL filtering rule on the firewall may prevent the MAGE handshake from completing with Exchange Web Services (EWS), autodiscover request, with the Office 365 cloud servers.
Exchange Web Services (EWS) is an API that enables client applications, such as MAGE, to communicate with Exchange Online. MAGE posts a SOAP request to Exchange Web Services (EWS) to retrieve information on Exchange accounts. Be sure to check the firewall rules are configured to allow full communication with Office 365 and the EWS services.
Another quick way to check if the firewalls devices may be blocking communications is to check the "Drops" record of the device. This will usually state what communication packets have been dropped by the device and revealing the issue.