Nastygram

nasty -gram. Possibly a playful variation of candygram.

Full definition of nastygram

(plural nastygrams)

(informal) A written communication containing unpleasant material, especially one that criticizes, insults, or intimidates the recipient.

1987, Steve Kerch, "Realty Terminology: Bird dogs to fat cats," Chicago Tribune, 24 Jan., p. 7:Ordinary people might find a "nasty gram" in the mail, a notice from a lender who has not received payment from a borrower.
2008, Nate Anderson, "Cash, not idealism, behind ISP embrace of music biz," Ars Technica, (retrieved 10 Feb 2009):Virgin Media, one of the UK's largest ISPs, has agreed to forward British music industry nastygrams to subscribers suspected of illegal file-swapping.

Now often used to refer to unpleasant messages distributed by electronic means, such as by email or internet posting.