User name and password will be the same as your account for the default mail account, except it must be in the format of an email address. For accounts that you add via cpanel they will be as you set them at the time you set up the account. SMTP port 587 usually works just fine. For the server name, I have found that just using your domain name works just fine as well as proceeding it with mail. Most accounts now require that you authenticate the SMTP (outgoing mail) session. All this information should be in the welcome letter from LP.

For example if your account user name is mydom3 the email address would be mydom3@mydomain.com and the password is the same as your cpanel password. the server would be either mydomain.com or mail.mydomain.com