The most common reason for being unable to send mail is because the ISP in question is blocking Port 25. This is explained in detail in the following Knowledgebase article:
http://service.futurequest.net/index...details&_i=165
However, a quick test and workaround is to set the Outbound SMTP port to either 1025 or 587, as FutureQuest provides listening SMTP servers on these 2 alternative ports to provide a workaround for this problem.
Yes, it is necessary to authenticate to send outbound mail, which is also covered in the KB article linked above.