The RelayServer property is used to specify an alternate
mail server which will deliver messages for the current user.
Normally, when the SendMessage method is used, the
recipient address is used to determine what mail server is
responsible for accepting messages for that user. However, under some
circumstances this may not be desirable or even possible. For
example, many Internet Service Providers (ISPs) require that
customers send all messages through their servers and block any
attempt to establish a direct connection with another mail server.
Setting the RelayServer property to the host name or address
of the ISP mail server will cause all messages to be relayed through
that server rather than directly to the recipient.
Note that using a mail server as a relay without the permission of
the organization or individual who owns that server may violate
Acceptable Use Policies and/or Terms of Service agreements with your
service provider.