Examination of recipient's signing preferences yielded that the message should be signed using S/ MIME, at least for some recipients; however, you have not configured valid S/ MIME signing certificates for this identity.
O exame das preferencias de sinatura dos destinatarios revelou que a mensaxe debería asinarse empregando S/ MIME, ao menos para algúns dos destinatarios; porén, non ten configurado certificados S/ MIME válidos para asinar con esta identidade.