ARCHIVED: What are digital signatures, and how can I use them to sign my email messages?

Digital signatures are electronic signatures that verify that a message originated from the signer and that it has not been altered. They ensure that a message you're reading has not been changed since it was signed, and is not spoofed from a different sender.

Two common ways to digitally sign messages are S/MIME (or Secure MIME) and PGP (or later versions, e.g., OpenPGP, GnuPG, or GPG). In both methods, you use your private key (which you keep to yourself) to sign your message; then, the recipient uses your public key (which you share broadly) to verify that it was indeed you who sent it.