Hi @Brent Arias ,
Yes. we often receive a "mailbox not enabled" MailboxNotEnabledForRESTAPI because many users have not made their first/initial login attempt.
Please refer below Microsoft article to get more details on this case.
Please refer below Microsoft article to get all details of "user resource type"
So accountEnabled property is of "Boolean" type and if it is true then account is enabled; otherwise, if false then account is disabled. This property is required when a user is created. It Returned only on $select and it supports $filter(eq, ne, not, and in).
Hope this helps.
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