Ref+10, such defamatory emails/letters/calls could constitute libel, and if you have proof (i.e. can get hold of a copy of the letter/email or a recording of a phone conversation), it can potentially get very expensive for the originating person/company.
You could actually stand to make a healthy sum in the process if your lawyer can argue successfully that you incurred a loss (didn't get that jet job, lower entry salary/rank, etc.) as a direct or indirect result of the defamation.
I would never ever stand for something outrageous like that, it's unbelievable bad form, not to mention illegal, and I would encourage you and anyone else affected by such a horrible practice to seek legal representation and if possible sue the ba
rds for all you can!!
Also, if anyone has such proof, I would also encourage them (after checking with their legal representation) to post the contents here and so name and shame the companies and individuals involved.. that would teach them
BTW Ref+10 you can still take legal action years after the fact