Depending on which CA you go through, they may refer to it differently. It is usually Apache.
Cisco recommends that you obtain an X.509, or Privacy Enhanced Email (PEM) certificate from a CA. This might also be referred to as an Apache certificate. The certificate from a CA is desirable over the self-signed certificate because a self-signed certificate is similar to the previously mentioned demonstration certificate, which cannot offer a verifiable connection.
Note: The PEM certificate format is further defined in RFC 1421 through RFC 1424. The PEM is a container format that can include only the public certificate (such as with Apache installs and CA certificate files /etc/ssl/certs) or an entire certificate chain, to include public key, private key, and root certificates. The name PEM is from a failed method for secure email, but the container format that it used is still active and is a base-64 translation of the X.509 ASN.1 keys.
From the following:
http://www.cisco.com/c/en/us/support/docs/security/email-security-appliance/118844-technote-esa-00.html
-Robert
