In OE, you need to click Tools → Account → Mail → Account (select the email account for applying for certificate) → Properties → Security, and then click the selection buttons in the signing certificate and encryption preference section respectively, and select the certificate you applied for in the pop-up certificate list box. If you don't import the certificate in the encryption preference, you can't send the public key at the same time when you send the "digitally signed" mail, and when the other party doesn't receive the public key, you will also encounter the situation of "digital identity loss".

Suppose Party B sends a signed email to Party A now, then Party A should click the red signature icon on the right side of the email content in OE, click View Certificate in the pop-up properties window, and click Add to Address Book in the pop-up View Certificate dialog box. According to the instructions, it can be known that the encryption preference of the sender will be saved in the address book. Obviously, this step will keep the sender's public key in A's computer.