10.6.8 is Snow Leopard. Your sendmail server settings vary depending on the application for Mail. The built-in application, Mail offers SMTP without password through your internet access provider, or through other providers with password authentication. Whomever gives you e-mail access should have sendmail settings depending on whether or not they give you internet access or not. Who gives you e-mail access? Who gives you internet access?
Thanks for your prompt reply. My email provider is Yahoo!, and each time I try to send email through Snow Leopard, I get a prompt stating "Cannot send msg. using server smpt" ... Internet provider is Warner. I've even deleted the account I was using and started another one, but still to no avail. I may be typing in something wrong? Any help is appreciated!
It appears you might need a Yahoo plus account to utilize it as an SMTP server. The server address is plus.smtp.mail.yahoo.com
Other than that, I would contact Yahoo support directly. Ask them if they require password authentication. If they do, usually your e-mail address is your username. Often they require port 587, 2626, or 2662. Only Yahoo would know for certain which one to use.