Need to filter email that arrives with blank subject, blank sender and a ? in the date field. This mail is very annoying.

I tried putting blanks in the filtering but with no luck.

//This isn't a security question.
More details please. Any correllation possible from looking at the full mailheaders? What you're filtering with?

If you're looking for a blank header, you would match it with this:
^Subject:$
or if \s is a metacharacter for "whitespace" (space, tab, etc), you could use something like
^Subject:\s*$

Note that some legitimate e-mails are sent with no subject (sender was in a hurry, or forgot). The same method applies to the 822 From: header as well (note that all of these assume RFC822 headers).

For the date, something like this should work:
^Date:\s*\?\s*$

Oh, I should point out that all of this assume that your e-mail filter can use REGEX.