Customers have to know their Icewarp hostname eg; test.onice.io.
Perform an NSLOOKUP on the hostname to retrieve the cloud server IP address. (from command line 'nslookup test.onice.io'
Configure an A record for the webmail URL to point to the IP address retrieved through the NSLOOKUP process. ie; mail.domain.com
Configure an MX record for the domain name that points to the hostname used in the A record.
Configure an autodiscover record that points to the IP address ie; autodiscover.domain.com
Article here: https://www.icewarp.com/support/online_help/6480.htm
Configure an rDNS record for the ip address that was retrieved.
Article here: http://help.dnsmadeeasy.com/managed-dns/domain/setup-reverse-dns/