Protonmail frequently shows an inline file with standard suffix which it states preview is not supported. Many times these files are standard non-proprietary format (ie ISO 26300 or .odt or .ods). Yet, it does support and display proprietary files (ie Microsoft .docx).

This behavior is prejudicial and quite frankly a waste of time, bandwidth and storage to have to download to a temp storage location, find the file and where it was downloaded from LibreOffice/OpenOffice and reopen it.

It would be a straightforward program fix on files flagged as unsupported view types to permit the user to redirect the file to a program which can view the file, even on a read only basis. The present schema may leave files with sensitive data floating around a computer or force more users to proprietary formats run by big tech, which does who knows what with the contents in this era of pseudo Intelligence programmng.