Had a problem recently where my new host had placed sendmail elsewhere 
on their server than the usual usr/bin - this is how I got round it.
 
In the web_store_order_lib.pl
 

# mods to use server SENDMAIL.EXE 

$mailprog='c:\inetpub\scripts\sendmail.exe';

open(MAIL,"|$mailprog -t");

print MAIL "To: Catriona Wordsworth \n";

print MAIL "From: PureScents Website \n";

print MAIL "Subject: You have a new order!\n\n";

print MAIL "You have a new order from the website\n";

print MAIL "Yippee! - You had better get to it !\n";

print MAIL "Order ID : ",$time,"\n";

close(MAIL);

# end mods..

#

# &send_mail($sc_order_email,$sc_order_email,

# "Web Store Order",$time);

 

This way, once you have written in the new code to send the email via the real 
sendmail location you then need to cancel out the sendmail request in the sc_order_email 
variable.