Encrypted e-mail adds another security feature because it prevents a third party entity to see the actual content of the e-mail and it also protects sending of e-mail message thru an unsecure medium (e.g. a compromised wireless network).
Take note that you can't just encrypt any e-mail that you want to send. You also have to make sure that your recipients can decrypt the encrypted email you have just sent. This means that Encrypting an e-mail message with your own Digital Certificates and sending it out to your intended recipients will be useless, since you are the only one that can decrypt the e-mail that you have just sent. Your recipients cannot decrypt your email and thus would not be able to read it.
This also means that people who want to send you an encrypted email should have a copy of your public key. The public key is the one needed to encrypt emails that people want to send to you. If you want to send your recipients a copy of your certificate, all you have to do is send a signed email to them.
On the other hand if you have received a signed email, then you can also reply to that email and have it encrypted. When this happens you can follow the steps below to reply and encrypt a signed message: (for the sample purposes, the sender and the recipient below are the same).