CESNET PKI currently offers these types of personal certificates:
Personal eScience TCS certificates
Almost all email clients trust these certificates by default.
CESNET CA4 certificates.
CESNET CA4 is the successor of the CESNET CA3 certification authority operated by CESNET since 2011. Personal certificates issued by this authority are deployed where it is not possible or effective to involve the organization in the identity federation eduId.cz and thus to connect to the TCS Personal service. No electronic mail client automatically trusts CESNET CA4 certificates.