The user would therefore have the responsibility of either securely deleting the email or ensuring that its contents are not revealed to anyone else.

How to securely delete an object.

How to securely delete a subject.

An alternative approach, called key strengthening, extends the key with a random salt, but then (unlike in key stretching) securely deletes the salt.

As pointed out in a recent research article, there isn't a standard method for securely deleting data from a solid state drive.

We are thinking of using an eraser utility to securely delete sensitive files, overwriting them seven times.

With bleaching enabled, Window Washer can securely delete individual files, folders and contents of the Recycle Bin.

And it can securely delete files saved in Windows temporary folders.

Learn how to wipe a disk (and securely delete files)!

Follow up question: if you're not using an OS with trim support, is there a way to securely delete a file (so it's actually been deleted) on a SSD?