As pkh says there's no option in BE9.1 to authenticate to the SMTP server, however I can send you an email from my PC so Backup Exec can as well. The IP address the ISP has told you is the address for Outlook to send out through, what you need is the IP address of the ISP's server that recieves email for you.
Open dos prompt.
nslookup <cr>
set type=mx
yourdomain.com <-NOTE: no www
Non-authoritative answer:
yourdomain.com MX preference = 100, mail exchanger = mx1.yourdomain.com
mx1.yourdomain.com internet address = 10.23.42.11
That is the IP address to enter, in this example 10.23.42.11
Obviously you replace yourdomain.com with your own domain name and get a different IP address.
This gets past any outbound security of your ISP's mail server since you are creating inbound mail, if they have anti-spam filters on their inbound mail it might still get blocked but there is a fair chance of it getting through.
John