Certificate Authorities Sources of Free S/MIME Certificates Free certificates usable for S/MIME are available from: Actalis CAcert (CAcert is NOT one of the trusted authorities built-in to FireFox and ThunderBird. The connection is also untrusted) Comodo (They've changed their name to Sectigo and no longer offer free S/MIME certificates/) GlobalSign (No longer offer free certificates) InstantSSL (