No. The default Encrypting certificate and Signing Certificate is installed automatically once you setup your email account. They are called “Account Certificate” that are used to provide basic communication authentication and encryption service that you can’t delete it. And it is the default encrypting certificate and signing certificate before you import and set other certificate as default certificate.
However, you can import other certificate of you and set it as default encrypting certificate and the default signing certificate, and then they will be used for all email encryption and signing.