I receive s/mime signed email. Signature for this email is generated with certificate that is issued from this authority: Sectigo RSA Client Authentication and Secure Email CA expiration 01.01.2031 09c0f2fc0bda94db5ffe2bdfa89942cfc9e0ad00 Above certificated is issued from root authority, that is trusted by Thunderbird. USERTrust RSA Certificateio Authority expiration 19.01.2038 5379bf5aaa2b4acf5480e1d89bc09df2b20366cb
Thunderbird and other email clients can't validate this email signature. If i open the same email using Thunderbird in windows everything is ok.
I download an intermediate certificate. Then imported that certificated without trusting it(trust check-boxes are unchecked). Then that email signature can be validated.
Why intermediate certificates are not downloaded automatically in Ubuntu like it is working in Windows?
Is this way to add intermediate certificate is secure? For me it seems to be a secured way, because i don't give a trust to a certificate myself(unchecking trust check-boxes) but intermediate certificate is validated by the root certificate that is installed with Ubuntu.