We pick m.root-servers.net, one of the 13 root servers (1), and ask it about practicalcompserv.com and learn that com is delegated to 13 name servers (2), so we ask c.gtld-servers.net where we learn that practicalcompserv.com is delegated to two name servers, including ns3.orcsweb.com (3), so we ask that one and get the following answer:
The two mail servers backupmx and mailfilter.orcsweb.com together
There are several hundred of domains that use the two mail servers backupmx and mailfilter.orcsweb.com together, hereafter referred to as "mail server group 1".
Every fifth of them use the two mail servers backupmx and mail3.orcsweb.com together, hereafter referred to as "mail server group 2", (example: stringfaq.com, brantleycure.com and decimalcomputer.com ). Worth noting is that most of the domains that use mail server group 2 use name server group 1.
Every fifth of them use mail server group 1 (example: andersencpa.com, bmugroupinc.com and howtosur.com ). Worth noting is that two thirds of the domains that use mail server group 1 use name server group 1.
The mail server backupmx.orcsweb.com
There are almost a thousands domains that use the mail server backupmx.orcsweb.com.