The only thing you can do to truly delete data is destroy the drive (and in a manner that it can't be pieced back together with fragments of data recovered). Some "thermonuke" drives which is dangerous, as it involves placing the drive in a corrosive chemical solution that could become unstable and incendiary. However, Clinton would have been in trouble if she had destroyed the server. Another less drastic method that sometimes works is to overwrite the data you wish to delete. However, with an email, that's a little tricky.
Baby to Hillary Clinton: put me down, I'm not voting for you!
Some online continue to paint Clinton as having committed treason. Once again, as much as I am not a fan of Clinton, due to her involvement with now incarcerated private investigator, Anthony Pellicano, there is no evidence she or her husband betrayed America by selling national secrets to the country's enemies, as some are trying to imply. Don't accuse someone of treason who did not actually commit that crime. It is a very serious allegation to make and in this case against a couple who has done a lot for America.
Government Investigators Raise The Tally Of Unprotected Hillary Clinton Classified Emails From 2 To 150
Hillary Clinton Admits She Lied About Emails In FBI Investigation As Agents Find Examples Of Her Breaking The Law