To stop TLS encryption for a particular domain as QMT will encrypt via TLS all SMTP traffic unless
   1) a remote MTA does not support it,
   2) incompatible encryption between MTA(s),
   3) and/or prohibition by either MTA,
 do the following:
   1) # nslookup -type=mx 'domain.tld'
        domain.tld     mail exchanger = 0 mx.domain.tld.
   2) # mkdir /var/qmail/control/notlshosts/
   3) # touch /var/qmail/control/notlshosts/mx.domain.tld

 This will stop all traffic to domain.tld from being encrypted.