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