Certificate file (MIME x-x509-ca-cert)
CER is a file extension for an SSL certificate file format used by Web servers to help verify the identity and security of the site in question. SSL certificates are provided by a third-party security certificate authority such as VeriSign, GlobalSign or Thawte.
MIME type: application/x-x509-ca-cert, application/pkix-cert, application/keychain_access
Learn more about CER files:
Brien Posey tells 'How to set up an SSL certificate to encrypt OWA and ActiveSync traffic'.
Get answers to certificate-related questions at IT Knowledge Exchange.