Hi,
Email had been relayed from Office 365 (Exchange Online) via Smart host defined to our organization’s email server (Exchange Server 2013).
If the mail flow has been configured correctly, you would be able to send from ******@Contoso.com (Exchange Online) sending an email to ******@contoso.com (Exchange Server 2013).
To send a copy to ******@gmail.com, you can create an Outlook inbox rule in ******@contoso.com's mailbox.
The rule would be like:
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