Hi @Sherazad ,
Could you please explain more details about the unc path that you mentioned?
Flow could save the email attachment with new name to sharepoint, Onedrive for business and also local folder with File System connector.
Make an example to save the email attachment in your Onedrive for business as below:

The expression in the Compose as below would get the attachment extension:
last(split(items('Apply_to_each')?['Name'],'.'))
The expression in the File Name column as below would rename the attachment with name "New Name":
concat('New Name.',outputs('Compose'))
The flow would run successfully as below:


Best regards,
Community Support Team _ Alice Zhang
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