You work as the network administrator at Domain.com. The Domain.com network consists of a single Active Directory domain named Domain.com. Domain.com has its headquarters located in London and branch office located in Paris. All servers on the Domain.com network run Windows Server 2008 and all client computers run Windows Vista. Domain.com currently makes use of a computer named CERTKILLER-SR01 that is configured as the network public DNS server. Domain.com additionally uses a computer named CERTKILLER-SR02 configured as an e-mail server.
During the course of the day you receive complaints from client computers on the external network
that they are unable to send e-mail messages to the Domain.com network. Whilst doing routine maintenance you discover that a host (A) DNS record exists for CERTKILLER-SR02 on the external computers. Domain.com wants you to ensure that CERTKILLER-SR02 is configured correctly to receive e-mail messages.
What should you do?
A.
You should consider having a Service Location (SRV) record added for CERTKILLER-SR02.
B.
You should consider having a Canonical (CNAME) record added which maps CERTKILLER- SR02 to Domain.com.
C.
You should consider having a Mail Exchanger (MX) record added for CERTKILLER-SR02.
D.
You should consider having a Mailboc (MB) record added for CERTKILLER-SR02.
Explanation:
You should then set the Service field to _smtp and the Protocol field to _tcp using Port Number 25.
You should then set the Mailbox Host setting to CERTKILLER-SR02.
In the scenario you should consider having a Mail Exchanger (MX) record added for CERTKILLER-SR02 to ensure that CERTKILLER-SR02 is to receive e-mail from external client computers. You should additionally note that the MX record controls the way e-mail is delivered and are particularly used to locate the receiving mail servers for a given host with the order of priority of these mail servers. You should also remember that non-RFX-compliant server fail to deliver e-mail for domain which lack MX records which includes certain versions of Microsoft Exchange.
In the scenario you are aware that host (A) DNS records are available to the external client computers soo configuring the Mail Exchanger record for CERTKILLER-SR02 defines the destination host record for the mail server. You should finally note that the destination mail server record uses the host (A record not a CNMAE or IP address.
Reference : E-mail, Mail Exchangers, and DNS
http://www.dyndns.com/support/kb/email_mail_exchangers_and_dns.html