By encrypting an email you make sure only the recipient will be able to read it. By signing an email the recepient knows the mail was sent by you. This is an important distinction because there is no other way to make sure an encrypted email really originates from the sender.
- Configure your mail client with a fake identity, using a real domain name like protonmail.com. In thunderbird it can be done via Settings > Manage identities
- Compose an email and select this fake identity. Also use Options > Encrypt to encrypt the content. But do not try to sign it: you won’t be able to because you do not have a private key for that fake email.
- When the recipient reads the email, a green tickbox next to the encryption logo shows.
- If they click on it to verify the information, it will show that it is indeed encrypted for you. It will also show that it has not been signed by the sender.