Recently I have been noticing email showing up in my held mail folder that have no dates or email addresses. When I attempt to report as spam, I get message that IP address can't be found. Is this a new spammer trick?

certainly nothing "new" in what you're describing. Forging and screwing up lines is a trick of the expert spammer, but also an experience offered by the clueless spammer with shoddy spammer software .... sometimes hard to tell the difference <g> ... but. to talk to "your" spam issue, one needs to see the headers of the spam in question.

...Also see FAQ Entry: "Header incomplete, aborting." and "No, source IP address found, cannot proceed.. Or, maybe not -- it doesn't add a lot to what Wazoo wrote, above. <g>