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.
rest-api-is-not-yet-supported-for-this-mailbox-error
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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