Roady said:
You can create a "reverse" rule which moves all messages to the Junk E-mail
folder unless the sender's address contains "a", "e", "i", "o" or "u" (you
can add some additional characters as well of course but this should cover
it for most if not all regular addresses).
But the sender might be using something like (e-mail address removed) for their
mailing address which doesn't have any vowels in it. So to check for a
blank Subject header, I check for the absence of a-z and 0-9 and for
checking on a blank From header I look for the absence of the @
character (which serves double duty as noted below).
Move or delete except if @ in sender's address
- If the sender's e-mail was empty, it wouldn't have the @ character.
- If the @ character is missing, it isn't a valid e-mail address.
Rather than delete the suspect message, I move it to the Junk folder. I
then use auto-archive to permanently delete items in the Junk folder
that are over N days old (I set it to 3 days).