This rule identifies email with an undisclosed sender address, sometimes the sender address is undisclosed in SPAM email, almost never with legitimate email
Some mailservers send out of office replies and NDRs from a blank sender address. SMTP therefore has to accept this. Email with blank senders that are not from your network OR Out Of Office replies or NDRs can be blocked as spam
This rule identifies email where the sender address contains odd or invalid character sequences. Legitimate email addresses rarely contain such characters
This rule identifies email where the displayed From name tries to hide the actual email address using a displayed name of an email address that differs from the actual email address
such as "a@b.com" <x@y.com>