This type has been deprecated in favor of one of it's alternatives. While you should likely still support it, it should not be your first choice if assigning a MIME type.
Instead please use application/pkcs7-mime

Used in file types
  • .p7c
  • .p7m
This type may also appear as
  • application/x-pkcs7-certificates
  • application/pkcs7-mime
Further reading
  1. IETF - Internet Engineering Task Force (RFC 5273)

  2. PKI Tutorial