From Client Security's E-mail scanning settings, we see Action on malformed message parts,
what is the definition of "malformed message"?
Can someone give an example about this?
Email messages can be malformed in a number of ways. Various of the header fields (source, destination addresses etc.) can be corrupted, either accidentally or deliberately. The format used to encode email attachments can also be subject to corruption. Quite often, malicious, spam and phishing emails are deliberatly malformed to avoid detection by security products. For example, those emails can contain binary data in text headers, use out-of-spec line lenths, mixed CR/LF combinations, embed quotes in attachment names, etc.
Hope this helps.