use S/MIME with Thunderbird

I would like to use S/MIME with Thunderbird.

https://support.mozilla.org/en-US/kb/thunderbird-help-cannot-encrypt#w_matching-email-address

Thunderbird usually requires that the inner structure of the key or certificate lists the exactly matching email address. It allows Thunderbird to automatically decide if a public key or certificate can be used for an email address.

So it can be impossible to use certificats from Tajine because all inner structure is uppercased. And mail are written often downcased, like in Thunderbird configuration.