Attachments appear as Hotspot in Domino with a value of 10 (unknown) instead of 4 (file)
Open the Global Default settings
Find the [Exchange] section
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Enables or disables the option of extracting images from Notes messages and replacing them with OLE Device Independent Bitmap object attachments. This option makes images renderable in both OWA and the Office web client, and also improves image compression by a factor of two.
This can be found in the MNE_4.12.1_ProgramParametersReference.pdf by searching for ExtractEmbeddedImages