I tried to encrypt an email message (S/MIME) using ECC NIST P-256 key (with matched X509 certificate) that is stored on smart card applet but I have got error: "Sending of the message failed. Unable to encrypt message. Please check that you have a valid email certificate for each recipient. Please check that the certificates specified in Mail & Newsgroups Account Settings for this mail account are valid and trusted for mail." I tried to encrypt message to myself (i.e. sender and receiver are same). I used Thunderbird 91.8.1 (64-bit) at Windows 10 64-bit PC. The smart card applet has implemented pkcs11 interface. I could sign email message (S/MIME) using the same ECC NIST P-256 key (with same X509 certificate) successfully. Does Thunderbird support encryption of SMIME email message using Elliptic Curve Cryptography (for example: ECC NIST P-256 or ECC NIST P-521)? If so what I need to set up in Thunderbird in order to have enabled SMIME message encryption using Elliptic Curve Cryptography. Thank you in advance!