此使用者的本地郵箱尚未遷移到 Exchange Online

This user's on-premises mailbox hasn't been migrated to Exchange Online. The Exchange Online mailbox will be available after migration is completed.

如何在不設置混合環境的情況下預配郵箱？

使用同步規則編輯器將雲中的 msExchMailboxGUID 屬性設置為 NULL，同時在本地保持不變。

https://support.rhipe.com/portal/en/kb/articles/how-can-i-set-msexchmailboxguid-attribute-to-null-1-10-2019#Answer

引用自：https://serverfault.com/questions/1099511