smime-crl-check

smime-crl-check is a variable defined in `smime.el'.
Its value is

nil

Documentation:
*Check revocation status of signers certificate using CRLs.
Enabling this will have OpenSSL check the signers certificate
against a certificate revocation list (CRL).

For this to work the CRL must be up-to-date and since they are
normally updated quite often (i.e., several times a day) you
probably need some tool to keep them up-to-date. Unfortunately
Gnus cannot do this for you.

The CRL should either be appended (in PEM format) to your
`smime-CA-file' or be located in a file (also in PEM format) in
your `smime-certificate-directory' named to the X.509 hash of the
certificate with .r0 as file name extension.

At least OpenSSL version 0.9.7 is required for this to work.

You can customize this variable.