We pick b.root-servers.net, one of the 13 root servers (1), and ask it about rosecrest.org and learn that org is delegated to six name servers (2), so we ask a2.org.afilias-nst.info where we learn that rosecrest.org is delegated to two name servers, including ns19.worldnic.com (3), so we ask that one and get the following answer:
Three quarter of them use the two mail servers mx1 and mx2.lhomes.iphmx.com together, hereafter referred to as "mail server group 1". Worth noting is that all of the domains that use mail server group 1 use only the IPv4 number 174.121.46.130.
All of the several thousand of domains that use the primary name server ns19.worldnic.com use name server group 1 (example: slcpdox.com, povagus.com and pharmascoop.net ). Worth noting is that every fifth of the domains that use name server group 1 use the primary name server ns19.worldnic.com.
The two mail servers mx1 and mx2.lhomes.iphmx.com together
There are about twenty domains that use mail server group 1.
All of those use only the IPv4 number 174.121.46.130. Worth noting is that three quarter of the domains that only use the IPv4 number 174.121.46.130 use mail server group 1.