DNSHostname is used important for mail delivery, and is
needed only if Hostname property is
not set. wodSmtp will try to fill this value during its
initialization (it will get information from the registry),
but if it fails you need to fill it by yourself.
It should point to Nameserver address wodSmtp should use
to find default mail exchangers of the recipient. Again -
if you set Hostname property, message will be delivered
through that hostname and there is no need to set
Nameserver, because wodSmtp will never send any DNS
Typically, wodSmtp will try to find "MX"
record for the recipient's domain, or possibly
"A" record if applicable.