What attachments are considered unsafe?
Javascript (.js)
Executables (.exe)
Java-Applets (.jar, .jvm)
Batch-Scripts (.bat, .cmd, .ps*)
Visual Basic Scripts (.vbs)
Dynamic files (.pif, .lnk, .shs, .shb)
Wordfiles (1997-2003) (.doc)
Excel files (1997-2003) (.xls)
Office Macro Files (.docm, .xlsm)

How do I know if an attachment has been removed?

Instead of the Attachment, you will find a ATTACHMENT_REMOVED.txt File in your Email.

What can I do when an attachment has been removed?

You need to contact an administrator for your Organisation.