My provider does not accept mail from addresses without reverse DNS. When IP 18.104.22.168 tried to send mailhost confirmation messages they did not arrive. Some time later they were sent from a different IP and then they arrived. host 22.214.171.124 126.96.36.199.in-addr.arpa domain name pointer sc-app3.spamcop.net. host 188.8.131.52 Host 184.108.40.206.in-addr.arpa not found: 3(NXDOMAIN) Can Spamcop please arrange reverse DNS for this IP?