gnutls
exim -DSERVER=server -bd -oX PORT_D
****
-client-gnutls 127.0.0.1 PORT_D
+# Have the client prefer RSA (but support ECDSA as well). That should get us RSA on both older and newer GnuTLS.
+client-gnutls -p NONE:+SIGN-RSA-SHA256:+SIGN-ECDSA-SHA512:+VERS-TLS-ALL:+ECDHE-RSA:+DHE-RSA:+RSA:+CIPHER-ALL:+MAC-ALL:+COMP-NULL:+CURVE-ALL:+CTYPE-X509 127.0.0.1 PORT_D
??? 220
ehlo rhu.barb
??? 250-
quit
??? 221
****
-client-gnutls 127.0.0.1 PORT_D
+client-gnutls -p NONE:+SIGN-RSA-SHA256:+SIGN-ECDSA-SHA512:+VERS-TLS-ALL:+ECDHE-RSA:+DHE-RSA:+RSA:+CIPHER-ALL:+MAC-ALL:+COMP-NULL:+CURVE-ALL:+CTYPE-X509 127.0.0.1 PORT_D
??? 220
ehlo rhu.barb
??? 250-
quit
??? 221
****
-client-gnutls HOSTIPV4 PORT_D
+client-gnutls -p NONE:+SIGN-RSA-SHA256:+SIGN-ECDSA-SHA512:+VERS-TLS-ALL:+ECDHE-RSA:+DHE-RSA:+RSA:+CIPHER-ALL:+MAC-ALL:+COMP-NULL:+CURVE-ALL:+CTYPE-X509 HOSTIPV4 PORT_D
??? 220
ehlo rhu.barb
??? 250-
starttls
??? 220
****
-client-gnutls HOSTIPV4 PORT_D DIR/aux-fixed/exim-ca/example.com/server2.example.com/server2.example.com.pem DIR/aux-fixed/exim-ca/example.com/server2.example.com/server2.example.com.unlocked.key
+client-gnutls -p NONE:+SIGN-RSA-SHA256:+SIGN-ECDSA-SHA512:+VERS-TLS-ALL:+ECDHE-RSA:+DHE-RSA:+RSA:+CIPHER-ALL:+MAC-ALL:+COMP-NULL:+CURVE-ALL:+CTYPE-X509 HOSTIPV4 PORT_D DIR/aux-fixed/exim-ca/example.com/server2.example.com/server2.example.com.pem DIR/aux-fixed/exim-ca/example.com/server2.example.com/server2.example.com.unlocked.key
??? 220
ehlo rhu.barb
??? 250-
****
#
#
-# Make ECDSA authentication preferred (normally RSA is, it seems).
+# Make ECDSA authentication preferred (Older GnuTLS prefers RSA, it seems, Newer, ECDSA).
client-gnutls -p NONE:+SIGN-ECDSA-SHA512:+VERS-TLS-ALL:+KX-ALL:+CIPHER-ALL:+MAC-ALL:+COMP-NULL:+CURVE-ALL:+CTYPE-X509 127.0.0.1 PORT_D
??? 220
ehlo rhu.barb