On macOS and iOS, some eM Client users experienced SMIME certificates error “unknown revocation status.” This also affected some HTTP services, such as the automatic translation.

This is caused by the fact that Apple’s system does not always properly handle certificate revocation checks after Let’s Encrypt deprecated Online Certificate Status Protocol (OSCP) method in favor of Certificate Revocation Lists (CRL). We suspect that Apple does not take CRL into account at this time and since OCSP is no longer available, the status is left "unknown."

eM Client offers a setting, IgnoreUnknownRevocationStatus, to control this behavior now, which has 3 options:

The default behavior since eM Client 10.3.2298 will now ignore this specific error, but you can use these commands to change it:

To explicitly allow SMIME certificates to work, run this command in the terminal:
defaults write com.emclient.mail IgnoreUnknownRevocationStatus -int 1

To Enforce strict validation (this might also block other HTTP services, including eM Client's translation, QR Import, EWS Servers and more):
defaults write com.emclient.mail IgnoreUnknownRevocationStatus -int 0

To return to default behavior:
defaults delete com.emclient.mail IgnoreUnknownRevocationStatus