what is unknown error -5938?

what is unknown error -5938?

I am trying to send mail via the Linux command line:

#!/bin/bash
echo "nail test" | nail -v -s `dnsdomainname`" zoho smtp test subject" \
-S smtp-use-starttls \
-S smtp-auth=plain \
-S ssl-verify=ignore \
-S smtp=smtps://smtp.zoho.com:465 \
-S from=xxxx@zoho.com \
-S smtp-auth-user=xxxx \
-S smtp-auth-password="hahahahaha" \
-S nss-config-dir=/home/linuxutil/mailcerts/ \
yyyyy@zoho.com


Gives me:

250 AUTH LOGIN PLAIN
>>> STARTTLS
220 Ready to start TLS
SSL/TLS handshake failed: Unknown error -5938.

Anyone know what causes this?

Many thanks,
-T