e-mail settings for e-Newletter

I’m not terribly adept at setting up e-mail yet, and am having problems getting this to work. I have a LAMP VPS server, I am sending e-mails from a site located on that server, but it keeps throwing errors. I originally had a successful bounceback test, but now that is failing also.

Any ideas what I should be putting in those fields? I have e-mail accounts on the server, and they do work.