Hi ,
Which type of license you bought?
Does the problem of unavailability occur in the direction of Exchange? If so, are there any specific problems or errors?
Based on my knowledge, even though users don't need to be connected to the internet all the time to use Microsoft 365 Apps, users must connect to the internet at least once every 30 days. This is so that the status of their Office 365 (or Microsoft 365) subscriptions can be checked. If users don't connect within 30 days, Microsoft 365 Apps goes into reduced functionality mode. After users connect to the internet and their subscription status is verified, all the features of Microsoft 365 Apps are available again.
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