The To property returns the list of addresses that
received a copy of the current message. If there is no current
message, or the To header field is not defined, then this property
will return an empty string.
Setting the To property creates or changes the value of
the To header field in the message and specifies additional
recipients of the message. Multiple addresses may be specified by
separating them with a comma. Each address must conform to the
standard Internet address format.