It seems there are the programs ssmtp and msmtp which are similar in style to fake sendmail in windows why not include one of them with XAMPP for Linux, so it's easier to setup php mail in xampp for Linux?
Of course I note that you have your profile saying you run Windows 7 with 'your' XAMPP... If that's wrong, please fix - If you run XAMPP on multiple platforms (as I do) list both/all
I have taken your post as a suggestion, rather than a support request asking for help in setting up the native Linux/unix sendmail utility. I have asked for comment on that suggestion and pointed to this topic.
If that is not the case, just start a topic like 'Help setting up sendmail'