Our ISP is blocking port 25 so we are sending mail out using relay. Where do we set up authentication? I am under the "servers "tab in "MTA" under "network." Is this the right place to set it? If so, how do we set up? There is no section for authentication or to put in an email address to authenticate..

host outgoing.verizon.net[xxx.xxx.xxx.13] said: 550 5.7.1
Authentication Required (in reply to MAIL FROM command)

ANY help is appreciated! Not sure what I am doing!

Ubuntu 8.04 with Zimbra 6.06 Thanks.