Did you click on the "Click Here to Find Similar Threads" button, just below your title, when you posted this?
See the "Similar Threads" below, at bottom. Do any of these help?
Did you try Google.com? What links did you find? The above link is the first result that a search of your title found for me.
Tell us more about your computer, etc. Did you just install? Which version?
Did you do anything to configure sendmail? Post details of what you tried.
Thanks and welcome!