Fernando,
I found the following at the AOLserver doc (http://aolserver.com/docs/devel/tcl/api/general.html#ns_sendmail):
<q>ns_sendmail uses the SMTP server specified by the MailHost parameter in the configuration file. If MailHost is not specified in the configuration file, localhost is used. You can also specify an SMTP smarterhost in the SmtpPort parameter in the configuration file. </q>
Since "mailhost" parameter is in the ns/parameters section, I guess you need to add the "SmtpPort" in the same one.
Hope that will work.