A digital signature is a more robust electronic equivalent of your signature on paper. Technically a digital signature is a scrambled summary of a document. It is generated by a mathematical formula and a person’s private key.
If validated, the digital signature will:
Confirm the integrity of the message
Authenticate the signer, because only the signer has the private key, the message cannot be refuted as having been signed If someone does attempt to alter/interfere with a digitally signed message it will cause the automatic verification process to fail.
The email program you are using will tell you that a message has been digitally signed, who signed it, and whether the signature is valid.
The program recalculates the summary and compares it to the unscrambled summary from the email. If these are the same, then the signature is valid.