Why can't I send encrypted emails after installing an S/MIME certificate?

S/MIME encryption relies on a public key exchange mechanism.

• You must first send a signed email to the recipient; only after the recipient receives and saves your public key can they send encrypted emails to you.
• Similarly, you must also have the recipient's public key stored before you can send encrypted emails to them.

In short, both parties need to exchange public keys via signed emails first, before they can normally send and receive encrypted emails.