What is the issue?
Legitimate email with the MIME type application/octet-stream is being blocked as "Banned".
What causes the issue?
The application/octet-stream is a MIME type that is generically used for attaching several types of files to messages, including:
Executables (including viruses)
.doc and .xls files (including those with viruses)
.docx and .xlsx files (that are legitimate)
.pdf files (that are legitimate)
.ZIP and other archives
Given the generic nature of this MIME type, it should never be used to block or allow in Content Filtering > Attachment Mime Type Filters.
What is the solution?