Hi @Sai Manasa Chintakunta ,
Is your environment a Exchangne hybrid deployment environment?
According to your description, do you mean that the same AD account has both an on-premises Exchange mailbox and an O365 mailbox? If so, based on my knowledge this is not feasible. It will create mail flow issues. Please following the steps in the below link to recover. In order to protect the mailbox data, please backup the mailbox before operation.
Please refer to: How to recover when a mailbox exists in both Exchange Online and on-premises and My user has a mailbox both on-premises and in Exchange Online. Help!
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