About Mail() , Please Help Me!

Dear All
I Install VBulletion In Linux + Sendmail + Mysql + php 4.1
EveryThing is OK,
But Have Some error To me
The Error is "I Can Send Mail To My Users and include Email Notification"
The Error is not have any error code
and I Configure /etc/php.ini
and Setup sendmail -i -t
and In My Site Mail() is Can Work
But in VBulletion , Can not Sendmail To user .
So .....
Please Help Me !

Mark Chen