Thank you Jose, but a few days ago I solved with the following conf file
[thunderbird<->stunnel] cert = /etc/stunnel/stunnel.pem sslVersion = TLSv1.3 accept = 50050 connect = 127.0.0.1:50001
[stunnel<->xxxxxx] client=yes CApath = /etc/ssl/certs sslVersion = TLSv1 accept= 127.0.0.1:50001 connect=xxxxxxx:993
and in |/etc/crypto-policies/policies/modules/TLS10.pmod| inserted ===== protocol = TLS1.1+ TLS1.0+ min_tls_version = TLS1.0 hash = SHA1+ =====
then run command | # update-crypto-policies --set DEFAULT:TLS10| ||