go
mx-sec.crefisa.com.br has one IP number , which also has a corresponding reverse pointer. crefisa.com.br use this as a mailserver. crefisa.com.br is a domain controlled by two nameservers at terraempresas.com.br. They are on the same IP network. Incoming mail for crefisa.com.br is handled by two mailservers at crefisa.com.br themselves. They are on different IP networks. crefisa.com.br has one IP number. mx-sec.crefisa.com.br is hosted on a server in Brazil.

mx-sec.crefisa.com.br
a records
 
+ 200.231.64.3 200.231.0.0/16 AS4230 -
+ --- -

crefisa.com.br
a records
 
+ 200.205.208.90 200.205.0.0/16 AS10429  
+ ---  
ns-soa records
ns2.terraempresas.com.br
+ 200.154.46.8 200.154.0.0/16 AS11706 dns-teslave01-poa.terra.com.br
+ --- dns-teslave01-poa.terra.com.br
ns records
ns2.terraempresas.com.br
+ 200.154.46.8 200.154.0.0/16 AS11706 dns-teslave01-poa.terra.com.br
+ --- dns-teslave01-poa.terra.com.br
ns3.terraempresas.com.br
+ 200.154.46.9 200.154.0.0/16 AS11706 dns-teslave02-poa.terra.com.br
+ --- dns-teslave02-poa.terra.com.br
mx records
mx-sec.crefisa.com.br
+ 200.231.64.3 200.231.0.0/16 AS4230 -
+ --- -
mail.crefisa.com.br
+ 200.205.208.91 200.205.0.0/16 AS10429 -
ip numbers of host
200.231.64.3
ptrs of ip numbers
mx-sec.crefisa.com.br
ip numbers using ptr to this host
200.231.64.3
domains using this as mailserver
crefisa.com.br