What does signing an email do?

Question:

I mentioned the "tamper" proofing of the email.. I'm not completely familiar with the signature, but doesn't that only indicate who send it? But that does not "package" the email in a tamper-proof way??

Answer:

Signing an email does two things:

1) It verifies the identity of the sender.

2) It verifies that the content of the email (body + attachments) have not been modified.