Sorry for the delay and Thanks for your reply.
We found that EWS API can import and export email as a whole using a stream and now We can parse this stream and then set each attribute when writing the PST file by using Aspose API.
So We want to know if we can use this stream to write item as a whole instead of setting each attribute by using Aspose API just like EWS import API, if yes it will be more useful and easier.
We suggest that you can use the EWS editor tool to get the item stream.
Here is the download link of this tool:
Here is the guide EWS Api.docx
I hope it will be helpful for you.
BTW: The Redemption API also supports import stream, please refer to this link:
IImportExpotr interface (dimastr.com)