Forum Discussion
Online Calendars not working for Non Internet Users
we use Microsoft Exchange 2019 on premise and have been migrating resource calendars to the O365 Microsoft Exchange. We have a few sections of network that we keep off the internet on purpose. Those ...
Short answer is no. Once migrated to EXO, the on-premises mailboxes need internet access to connect to the EXO based mailboxes to interact with the calendars. You can try proxies and other methods, but that is an implementation that your organisation needs to decide on (Microsoft recommend not using proxies and allowing direct connections to the M365). Details on the required network URLs and IP addresses can be found here: https://learn.microsoft.com/en-us/microsoft-365/enterprise/urls-and-ip-address-ranges