Weird - I use Mandrake 8.1 too - but the MTA mine is using is postfix, not sendmail.
I'd recommend changing over from one to the other for a number of reasons :
1) Sendmail is pretty decrepit. It's been around for donkeys years and was never written with the evils of the modern internet in mind. It's had a lot of vulnerabilities exposed in it over the years - and has more patches than a rubber ring being used by a porcupine to go swimming...
2) The configuration for it is a nightmare. No understatement here. You have to write a Meta-config file (itself not very pretty), which is then processed by a macro language which turns it into the real config file for Sendmail because the real config file is too complicated for a human to write. That is the worst thing I've ever heard
3) Postfix, the other MTA which comes with Mandrake 8.1 - is easily configurable from the GUI using the WizDrake tools - so you don't have to get down and dirty with the actual config files itself...
That being said - whichever MTA you go for, Sendmail, QMail or postfix, they all work pretty much automagically. Your mail client shoves mail in it's direction, and the MTA hurls it feet first at the internet - without you having to do much....
Bry