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:

  • Images

  • 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

  • others

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?

  1. Go to Content Filtering Attachments > Mime Type Filters.

  2. If application/octet-stream is listed in the Mime Type column, delete the entry by clicking the Delete icon in the Options column.

  3. Click Apply.