when someone send you an email and hide the recipient names to defame you how can we prove legally because we can't see the recipients names

A lawyer is not qualified to help you find out the technology solution to uncovering the recipients' names. Legally, after a plaintiff sues a defendant, the next thing that happens is that both sides send each other demands for answers to written questions and demands for the production of documents. Your lawyer could start with a demand for the names, addresses, email addresses, and phone numbers of every person to whom the defamatory statement was sent. Defamation is very hard to prove. Opinions are not defamation. Truth, even partial or exagerated, is a complete defense. Damages are real problem. How were you injured by the statement? Did you lose a job, promotion, raise, customer, or contract? Were you upset enough to have seen a doctor or psychologist? The lack of damages is the reason defamation cases are rarely pursued by lawyers on a contingent fee basis. The cases where a celebrity sues for defamation and is awarded a dollar in damages, cost the celebrity more than $100,000.00. Such people are rich enough to be able to afford it. Dana Sack