Hi, @WongYK
To retrieve attachments larger than 5MB using Exchange Web Services (EWS), you first need to make sure that your Exchange server is configured to support larger attachments. This may involve updating certain settings on the server side, but this is usually handled by the Exchange administrator. The configuration settings include parameters such as 'MaxSendSize', 'MaxReceiveSize' and 'MaxAttachmentSize'.
Unfortunately, the “Exchange Server Management” tag currently focuses only on mail and mail flow, not code.
You can refer to exchange server - How to download >1 MB Email attachment using EWS in C# - Stack Overflow
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