You may be able to identify the IP addresses and machine names for the firewall, and the names of internal mail servers by:

You may be able to identify the IP addresses and machine names for the firewall, and the names
of internal mail servers by:

A.
Sending a mail message to a valid address on the target network,and examining the header
information generated by the IMAP servers

B.
Examining the SMTP header information generated by using the –mx command parameter of
DIG

C.
Examining the SMTP header information generated in response to an e-mail message sent to
an invalid address

D.
Sending a mail message to an invalid address on the target network,and examining the header
information generated by the POP servers