The MailExchange property array returns the host name of
the systems designated as the mail exchangers for the current domain.
The mail exchange hosts are returned sorted in priority order, with
the higher priority mail servers being listed first. The property
array is zero based, which means that the first index value is zero.
The HostName property must be set to the domain name that you
want to obtain the mail exchange records for.
This property array is commonly used to determine which system is
responsible for forwarding mail within a domain. For example, if a
mail message is addressed to the user firstname.lastname@example.org, you
can determine the name of the server or servers responsible for
accepting mail for that user by setting the value of the HostName
property to example.com and then checking the
MailExchange property array. Note that it is possible that a
domain will not have any mail exchange (MX) records, in which case
you should attempt to to connect directly to a mail server running on
the host specified in the domain name portion of the address.