Questions about encrypted email

My usage environment is: macOS 14.5, on-premise Exchange, using S/MIME for certificate encryption.
When using the EM client, I can connect to the account, successfully receive emails, and open encrypted emails, but there is an error message: “Failed to check certificate revocation.”
When I use Apple Mail, everything works normally, and the Keychain is functioning properly. However, there are issues with the EM client, and sending encrypted emails is not successful.

Please guide me on how to proceed.

Thank you! Looking forward to your reply!

It could be that part of the certificate chain necessary for validation is missing, like the root or intermediate certificate.

If they are missing, you can get them from the certificate issuer, and install them in your keychain.

I have imported both the enterprise certificate chain and the personal certificate into the keychain, and it works fine in Outlook.
How to obtain intermediate certificates?Why Outlook doesn’t require intermediate certificates?

If all the certificates are installed then it could be that the revocation server can’t be reached or has some error as eM Client won’t allow you to use the certificate unless we know it hasn’t been revoked. The revocation server may not be reachable if you are behind a firewall, proxy or VPN. It can also happen if you have self-signed certificates, and don’t have your own revocation server.

There is another possibility though, and that is if you have an Elliptic Curve certificate. Generally we don’t support them.